Public transport in the cities is generally pretty good, but heading out to smaller towns and villages can be challenging, with a very limited (or non existent) bus service. (although, judging by many of the comments here it must be absolutely abysmal in the USA)
My tip for travel between cities in the UK is bus services like National Express, Megabus or Flix. Far, far cheaper than the train, and more reliable.
I have Tmobile and have an international plan, so I should be good
Strongly urge you to read carefully what they provide & how they charge for various usages. Have a friend who went on a vacation, was accepting calls/texts from Canada, ended up with a huge bill. Paying CAD$20 all in to get a local SIM for a full month of local coverage with no worries of any overages is HUGE peace of mind. I have a Free Mobile SIM from France. The SIM itself was free. 12.99 Euro a month = less than CAD$20 all in (no add’l taxes, fees). Use it all over the EU for huge amount of data & free in/out texts. In France unlimited calls in/out. VERY cheap calls internationally. Lots of similar plans in the UK.
Just use whatsapp/facetime/FB messenger for calls! Almost nobody uses regular phone lines these days!
Public Transport you can rely on for convenient transport on a day-to-day basis basically doesn’t exist outside the US outside of a handful of cities.
If you don’t already, use Rome2Rio to find out what your options are for getting from anywhere in the world to anywhere else in the world. It lets you compare the amount of time & rough estimate of the cost differences between the options. Such as flights, trains, buses, ferries, rideshare - whatever is possible. Keep in mind with flights: you will also pay to get to/from the airport AND you have to factor in the time spent at the airport.
Say you are trying to get to the Peak District from London: you can take a train and be there in 2 hours or a bus and be there in 4 hours. The train is 2X faster & more comfortable but probably 2X more expensive as well.
Also highly suggest you ask your Sit Host for the best way to get to them: they’ll know.
BTW between cities in the UK, you’ll find that National Express is a great private bus system. They have an easy on line calendar and it’s easy to buy tix ahead of time or on the spot. Flix Bus is a German company that does some routes in the UK (they are more common in the EU). Both of them operate out of airports as well as train stations.
IF you are landing at Heathrow Airport, the best way into the City of London is the tube (underground) and you can tap to pay.
IF you are landing at Gatwick you’ll probably want to use one of the private bus companies. Those companies also depart both those airports for cities all over the UK. Generally cheaper and sometimes faster than trains which may do more stops en route.
In Canada, because our driving licenses are provincial, you need to check that the province your license is from, has an agreement with the UK. If not, you might need an international license, to rent or get insurance, especially if your license is written in French.
Driving, is sometimes manual, sometimes automatic, so maybe check that before accepting a sit, if you’re not super comfortable driving on the other side of the road+manual.
If you want to go anywhere, trains and Coaches are great, so you don’t need to drive!
As a couple of people have mentioned, Google Maps - the ‘public transport’ option - will give you very accurate and up-to-date information about bus/train etc routes/times etc.
You can also set ‘leave at’ or ‘arrive at’ to check future public transport details. I travel around the UK a lot by public transport, and Google Maps is absolutely indispensable.
OR, the perfectly fine train from Gatwick Airport to London Victoria…
Yes but for someone unfamiliar with the system, it can be a surprise that a ticket on Thameslink from Gatwick Airport into London can be £14 (CAD$25) or it can be £20 (CAD$36)
The National Express offers lots of times @ £10.50 (CAD$19).
She sounds like she’s looking for economical options.
A train from Gatwick Airport into the City of London for CAD$36 vs a bus for CAD$19 is a CAD$17 difference: worth knowing!
We have done both, both are good. But once because of a delay on the Tube found ourselves on Thameslink paying CAD$72 for the two of us to get to Gatwick.
One of the reasons I like flying into Heathrow where it’s an easy Tube ride into London!
Appreciate all the tips & responses so far. I would be interested in countryside/rural sits. I do have a smart phone but I only ever use Wi-Fi on it. The flip phone is for emergencies only and has no data anyway. All I need at home. Outside Canada I guess I would be buying a SIM with a plan with data. Did that in the states last time.
I have never driven on the other side of the road; I suppose a rural area would be a lot better for getting used to that!
I am 1/4 English and have grown up watching British TV so, pretty sure the accents wouldn’t confuse me. Think I would probably pick one up myself in a few days as I have an ear for them! 
Good UK travel apps & sites include Trainline.com flixbus.com Nationalexpress.com splitjourney.com Rome2rio kayak.com (rental cars) as a few links. The general rule with UK travel is the earlier the better for deals. #publictransporttastic
Consider contacting your Canadian telecoms company and expressly disabling authorization for roaming calls, roaming sms and roaming data. Canadian telecoms firms tend to charge breathtakingly high daily roaming fees. Or physically removing Canadian SIM card before leaving Canadian airspace. Exception would be if you really need to use your (non-VOIP) Canadian cellphone number in UK.
I did 3 strings of UK sits in 2022, 15 sits in all. You’ve got most of the tips I’d offer. Add one more - there are a few houses that have names, not numbers. The what3words app solves that problem as it assigns a 3 word phrase to every 10 sq m place. Then you can put the words into google or apple maps.
And I’d encourage you to get a smart phone. Map software is so useful for getting around, bus schedules, ride shares, even paying for transit.
Some other useful apps -
Atlas Obscura - cloud sourced for finding unusual tourist attractions (all over the world, but lots in the UK).
Eatwith (also a www site) for food experiences with locals - lots of pop 1 night food experiences in London. A good meal and for a solo traveler a way to meet other travelers.
trainline - comprehensive train schedules and tickets throughout the UK. There is a service charge that you might not pay if you use each train op’s own site, but trainline even breaks multi-train journeys and finds sometime cheaper tickets by splitting the ticket. The ticket shows up on your phone. And if you are a senior, buy a senior card and load it to the trainline app and it saves your senior card and searches for senior prices.
I use US T-mobile for my cell phone and intl 4G data and text messages are inclulded so don’t need to buy sim card. But I think that is a feature of US plans only.
I don’t have a smartphone either. Is renting one easily done in the UK (or elsewhere that you know about) ? How does one even find such a thing ?
Just google Rent a smartphone in the UK
Actually I find it’s the opposite as many times when rural there are no lane lines, the roads are narrow and you have to use pullouts to pass, and with fewer cars on the road it can be easy to go the wrong way. whereas in a town the lines are painted and you can generally follow the person in front of you to make sure you are turning into the right place on the right side.
@ABGM I completely agree with @CreatureCuddler that rural driving can be far more hair-raising than on the motorways. As they point out, roads tend to be very narrow lanes with hedges right along the edges. Some have passing places but if you’re not near one and you see a tractor/grocery delivery van etc coming in the opposite direction, you then have to reverse until you find the last one. Or there is a 4WD coming and you have no option but to both try to squeeze past where there is a good risk you may get damage to the car, as I can attest to! I’m an Aussie used to driving on the left side and have rented a car each time I visit the UK annually since 2015 and, although I am used to the narrow roads, I still don’t enjoy driving along them!
Me neither, and I live here! On a recent sit up narrow, winding lanes, I took delivery of a new-to-me car which I discovered is wider than the one that it replaced - many eeek moments!
But driving these lanes is a bit easier at night because car headlights help you know what may be ahead. Unless it’s a pheasant (notorious for having no road sense) or a badger or deer.
One hazard in some areas is “lycra man”, especially on Saturday and Sunday, and strangely Wednesday, too. Cyclists seem to like the challenge of hilly, winding country roads. I cycle to get from A to B and respect their right to be on the road too, but it wears a bit thin after following one for several miles.
I completely understand those “eek” moments @DianeS and also those groups of cyclists!! Not good following them on those narrow roads and not being able to pass them.