Hi @Columbocat1 and welcome to the forum! On first read, I thought the sitter was asking so she would know how much to budget, in which case I would suggest using Google maps or Rome2Rio to figure out the mileage, then looking up the average price of gas/petrol and as they say in the UK, “Do the maths!” Rome2Rio also includes this info in its search.
But now I see she’s asking you to pay. Unfortunately, this is not part of the exchange here on THS nor is it permitted in the code of conduct. Is this sitter new? If not, s/he should already know this. If so you can inform her/him that this is not permitted.
Unless you feel completely comfortable following this exchange, my advice would be to unconfirm this sitter and resume your search.
As a new forum member, you can add your listing to your forum profile by following these instructions:
How to add your listing or profile to your forum profile
This will give you more exposure, as readers of the forum who might otherwise not have seen your listing will have a chance to see it and you will also be able to get helpful feedback from members.