That's great - everything's going to be just fine! I think leaving the kibble/treats just inside her box is OK - it'll help her associate your smell with food.
I think doing as much stuff as you can on a schedule for her right now will really help. The big barrier in socializing a feral/scared stray is that trust factor - and wanting nothing from them and meeting all their needs without requiring anything (including interaction) from them goes a loooooong way to crossing that barrier. Food is a HUGE motivator in that, and doing everything on as much a schedule as possible REALLY helps reinforce that YOU are the one providing for their needs without being scary or threatening.
Obviously spend whatever time in the room you can reading out loud, napping, sewing, singing, folding laundry - whatever - just letting her get used to you being uninterested in her and non-threatening. Doing whatever you can down on the floor with your side to her will help.
But scooping litter boxes, filling kibble - leaving little pile of kibble inside of box, putting out and picking up wet food, cleaning water dish - the more of a regular schedule you can keep to for all of that part of it, the more quickly she's likely to come around.
Also, knocking lightly on her door and telling her you're coming in is good too. If she was out of her box, it's less scary for her than if the door just suddenly opens.
...and if she's eating the kibble, I wouldn't worry about the A/D. It's that expensive prescription food you can only buy at the vet, and she doesn't really need it (and it's not very high quality stuff to begin with, so definitely over priced for what it is).
OH! Get a couple of t-shirts really good and sweaty. Once you know she's eating, leave one under her kibble dish. When you leave the room, put treats down on the other one. This will help her associate your scent with something she loves even faster.
You're doing great!
...I know - it's impossible not to worry. But she's hydrated for sure, and starting to eat, so everything will be just fine!
BTW - I don't remember the beginning of the thread. She's already spayed, right? But did she get a check-up? Are you sure she doesn't have parasites or anything?