As pp have said, keep on the same food and you can gradually change over time, same with the litter. I use wood pellets and scoop out poo and pee as & when, topping up if it gets low, with a full change every 2 weeks (to fit in with bin day!). I do leave dry out 24/7, as a) mine self regulate their food intake and b) they are grazers, so eat very little & often e.g. half a pouch at breakfast today (between 2 cats) is still only half eaten, rest will probably go in little bits during the day. Check with the rescue whether they seem to prefer wet or dry as cats, like humans, have different tastes.
Quiet room yes, but try to spend some time in there with her. Reading, watching TV, talking quietly etc. so she just gets used to your presence & voice. Let her come to you, don't push the contact.
Ideally 2 litter trays, preferably in a tucked away place so she feels safe there. Another vote here for Feliway or similar, works with the majority of cats.
Get good insurance, ideally with lifetime cover. One of mine has just been diagnosed with kidney failure and he will need blood tests, urine tests and BP checks every month for as long as he lives. This could be a few years yet, and lifetime cover means that he will get that paid for as long as he's with us and I only have to pay the excess once a year.
Watch Jackson Galaxy on YouTube. He is the ultimate cat whisperer and has loads of tips on settling in new cats, or resolving problems etc.
And finally remember the cat tax when you get her home - we need pics!