It takes a while for true dehydration to set in so try not to panic - it's too soon for that. 24 hour viruses don't cause that except in cases where something else has already been going on - they're miserable but not dangerous in most people.
Don't keep pushing anything but water until the stomach settles. I'm a nutritional consultant/educator, and we never recommend Gatorade due to all the dyes - they're terrible for you anyway, but they can irritate an inflamed stomach. Ginger ale is a good first choice but get something from the natural food section that does not contain high fructose corn syrup (regular) or artificial sweeteners (diet) which you don't want. You could also try a ginger tea or just putting ginger in warm water - but don't do anything until she's been vomit-free for 2 hours. Then do 1 ounce of liquid, no more. Wait 30 minutes, repeat. After more hours, go to 2 ounces.
Don't do anything right after she wakes up - the stuff that accumulates while she's been lying down can make things worse. You can also crush up some ice cubes and let her suck on the ice chips. The nausea can also be worse when the sugar level drops too much (think of pregnant women with morning sickness all day long - they get IVs with salt, sugar and water) so you can add a little regular sugar to whatever you can get her to drink, but don't start with that. And don't do any OJ or citrus, no cranberry (full of high fructose corn syrup), and no dairy at all for 2 more days. When it's time for food, do BRAT - bananas, rice, applesauce, toast (with a tiny amount of preserves but no butter).
This could progress from stomach to intestines, so if she gets diarrhea, I wouldn't be surprised. The treatment is the same.
I can't believe they kept her in the office all day long after 2 bouts of vomiting - that poor child should have been sent home. I wouldn't send her back until she has been free of vomiting, diarrhea and excessive sleepiness for at least 24 hours.