Hugs - I know this must be a worrying time for you.
Does she have "full-on" bloat or is it just the vet has seen gas in the intestines? Is her abdomen a bit swollen and when you tap it does it sound hollow?
Please do not. under any circumstances, feed her veggies, fruit or grass atm - they will make the problem worse.
Do you have any idea what she ate 24hours prior to the first symptoms as that could help identify what might have caused this?
FEEDING
The only way to get fibre/nutrition into a piggie with bloat is to syringe feed mushed up nuggets, preferably with a probiotic in it (or Oxbow Critical Care or Supreme Recovery)
Additional fluids (water) will also help. She will need approx 20ml every 4hours.
The syringe feeding guide is here
http://www.theguineapigforum.co.uk/threads/complete-hand-feeding-guide.115359/
MEDICATION
Has the vet given any gut motility drugs (by injection or orally). Something like metoclopromide or Reglan or (preferably) Cisapride? If not, do you have any Zantac (Ranitidine) in the house? (If so please reply to my PM). Gut motility drugs (pro-kinetics) are an absolute necessity for piggies with gas in the intestines as they help the stomach empty and intestines keep moving thus expelling the gas. If your piggie has not received any, then please go back to the vet when they open and ask for them to be given.
Has the vet given any pain relief? Normally this would be Loxicam (Metacam)
Please do NOT give Infacol/Simethicone or similar.....nor any liquid paraffin.
OTHER ASSISTANCE
Vibration/gentle massage can help shift the gas. I have a vibrating massage pad and also have taken my bloaty pigs for car journeys in the middle of the night to help move the gas further through the gut.
@Stewybus has a very good way of helping massage a piggie with bloat using an electric toothbrush so hopefully he will be on later to explain.
The most important thing is to keep putting food and fluids into her at regular intervals whilst letting her take them at her own pace (which will be slowly - no more than 0.5ml per mouthful). And then to ensure she is getting gut motility meds.
Providing it's not too serious, she should recover within 48hours. (NB No fruit/veggies for a few days afterwards as her tummy will be very sensitive. Then start introducing one by one - starting with grass/lettuce/dandelion/spinach/parsley/cucumber......gradually introduce baby corn/carrots...and finally try the brassicas (broccoli/kale etc) and fruit,
Hope this helps
x