My experience through part of my 20s was similar. Usually, I did it for minimal pay so long as there was food. Cats aren’t much work, and I’m sure she’ll appreciate the privacy more than anything. Plus, she probably can go home to eat if the pantry runs low. If you’re going to pay, I’d say $50—$75/ week should be sufficient, especially if there are other perks (cable, internet, etc.) I used to do it for $7–10/day. You can also supplement with a gift from wherever you’re traveling to. Definitely leave her the vet info & make sure she has the means to pay should an emergency arise.

i would give her $100 and bring her a nice gift/souvenir.

Will she vac, dust, mop and keep things tidy? If so, that is certainly worth a stipend.. Have you asked her? That is sometimes a good way of gathering info.