You can gently feel her crop, to see if there is any food in it.
If you aren't sure where the crop is, grab one of the healthy chickens: the crop is a bulge at the base of the neck, in the front but usually a little to one side. It's usually very full and bulgy at bedtime, some what full through most of the day, and empty when they wake up in the morning.
If her crop feels partly full at several points in the day, she is probably eating enough. If you check in the morning before the sun comes up, it should be empty--that shows that her digestion is working right.
Good plan. I assume her usual food is chick starter, and that's what you gave her? That's the best thing for her right now.
If she doesn't seem to be eating, try taking a spoonful of chick starter and getting it wet with water, so it's kind of sloppy. Chickens often like it that way. (If she won't eat it in a few hours, give it to the other chickens to finish up, before it has a chance to spoil.)
Hurt or sick chickens often sit around fluffed up and not doing much while they heal--rather like a sick person laying in bed.
It's probably best to turn on bright lights at least a few hours a day, to help her wake up and eat. But rest is important too, so be sure to turn off the lights at night
Chickens sometimes do heal from surprising injuries, if they are just provided with food, water, and a safe place to heal.
Meanwhile, don't forget about the others--if this one got picked on, then you don't want another one picked on tomorrow! It might help to give them some distractions--clumps of sod, a pile of weeds, some vegetable peelings, even a pile of fresh bedding to scratch through and spread around. The more time they spend scratching and looking for bits to eat, the less time they have for picking on each other. It also helps to have things they can sit on, and things they can run behind, and two or more feeders plus two or more waterers--so if the big chickens are hanging out by one, the little chickens can eat and drink from another.