@Kelownagurl I hope this helps as per the guidance but the app should notify you when you add to your favourites on both the app and the website.
For reference I just tested to see if a sit I just favourited then would cut across from the website to the mobile App and it did.
As soon as I put a heart on a particular sit on the website, I then logged out of my mobile App, logged back in to refresh and there was this sit now showing as favourited on my mobile App which I had only favourited through the website.
This thread is also helpful