It's the worst time of parenting, isn't it? You're caught in this vicious cycle of not being able to give her anything because she's vomiting. And there are no meds for a virus, it's true - plus she's not keeping them down.
It's completely normal for a fever to come back after a few hours. The fever is the sign of the body fighting the infection (whether it's viral or bacterial) and so the Tylenol only helps her be a little more comfortable for a while. Then it wears off. And if she's vomiting, she's not keeping it down anyway so it's of limited use. And if she's got a lot of goop from her nose and sinuses going down into her stomach, that's a real cause of upset too.
To help with the fever, you can do a cool (not cold) bath. You can also sponge her down with a wet washcloth if she doesn't want to sit in the tub. And be sure not to bundle her up so much that she sweats and overheats. Dress her as you dress yourself for the temperature in the room, or a little less if she's super hot.
The concern is dehydration, of course. But giving her a glass of water (which I am sure she wants - she's certainly thirsty) just makes her throw up. So she has to sip little by little. That's hard to do with a young child, so try ice chips and popsicles that she has to suck on a while to get anything down. But you have to give her just a little bit and then wait an hour to give her more. That will limit the vomiting.
After 4 hours with no vomiting, you can try a VERY SMALL amount of toast with fruit jelly. Little bites, no more than a quarter of a slice of bread. Then wait an hour. The sugar in the jelly, like the sugar in the popsicles, can help offset the drop in her blood sugar level from all the vomiting. (Same goes for pregnant women with morning sickness.) After an hour or more with no vomiting, you can try another piece, or you can try a few slices of banana, plus a few sips of water or part of a popsicle. If the popsicle is too hard for her to handle, make a few small pieces in ice cube trays with fruit juice (apple or cranberry, no orange due to the acid).
You didn't mention whether she has diarrhea, but sometimes these things "move down" in the child's body, especially with the phlegm in her stomach moving through her digestive tract. The classic bland diet for kids in this condition is "BRAT" - bananas, rice, applesauce, toast. Small amounts, every few hours. No dairy at all, including no cheese, and no butter on the toast. You can also try some chicken broth (for salt and fluids) or some plain Cheerios.
Please stay in touch with your daughter's pediatrician or the on-call pediatrician or nurse from that practice. Keep a food/fluid/temperature/vomiting log (with amounts and time of day) so you have it handy for this call. Let them advise you on whether you should go to the ER for IV fluids. I would avoid an ER on a holiday weekend if at all possible. You can also find out if there's an urgent care center near you - far preferable to an ER in most cases.