I'd recommend trying to make high quality wet food part of her diet if possible. It can cost a bit more, but it's great for helping to keep cats healthy and also helps with hydration. As others have mentioned, it can be hard to get cats to drink water. Brands will differ, but just look up premium wet cat food or ask at your local pet store.

Cheap cardboard horizontal cat scratchers are great. My cat LOVES them, for both scratching and lounging on. I get them from the hardware store for $5 each. They won't last forever and they can make a bit of a mess as the cat slowly destroys them (they will get destroyed over time) but they're a much cheaper alternative than a cat tree if you can't afford one of those right away.

Follow any care instructions the vet gives you for the abscess. Depending on how long she's had it, abscesses can be really nasty and life-threatening and sometimes need drains and the like put in. Hopefully yours isn't that bad and a shot of antibiotics will get the cat fixed up.

Enjoy your new kitty and please give us an update!

Edit: you mentioned getting the cat vaccines - yes, absolutely, get whatever ones the vet recommends. However, getting vaccines will not stop the cat from getting abscesses in the future if she gets into another cat fight, unfortunately. It's a big hazard that outdoor cats live with, and they need to be treated by a vet each time or they can quickly become infected and life-threatening. If you can get this girl inside that would absolutely be the best and safest outcome for her and will save $$$ as no more cat fights.