High WBC High Neutrophil Low Lymphocyte

My 16-y.o. has recently done a lot of gymnastics, weight-lifting and is running on little sleep.  4 days ago, she was sent home from school with vomitting.  I work for a clinic, so she came there.  She was running low-grade fever (99.5).  Gave her 25 mg. shot of Phenergan.  Didn't touch the vomitting.  Pain in upper right stomach area, just under her breast.  Took her to E.R.  WBC was 19.9.  Neuthrophils 91.8.  Lymphocytes 5.0.  Vomitting increased every 5 minutes and she was getting dehydrated, so IV started and she was given Zofran for the vomitting and later discharged with the pill version of the Zofran (which gave her severe headaches) -- only took that twice afterwards.  She did well on liquid diet, then bland foods.  Made mistake of drinking a chocolate milkshake yesterday and it soured badly on her stomach and she vomitted.  At that time, she complained of severe pain (like acid reflux) in her mid-chest/esophageal area.  Tums were chewed and she immediately began belching and had relief.  Started her on Prilosec 20 mg. b.i.d. and gave laxative/stool softener (noticed her bowels had hardly moved all week and when they did were very hard).  A day later (this morning) she had severe cramping in lower abdomen.  Bowel movement was hard and minimal, followed by diarrhea a few moments later and the abdomental pain stopped.  QUESTION:  Infection from stress to her body?  Possible gastroenteritis?  What to do with her now?