Friend hasbeen loosing weight constipated andcant keep food down and says her stomach hurts really bad?

Seek medical care. This situation could represent a bowel obstruction which can have many different causes. Depending on the age, previous surgeries or medical problems, obstructions can be caused by scarring, congenital defects, hernias, tumors, or twisted bowel (volvulus). Also inactivity of the bowels ( ileus) can be a cause. The vomiting could lead to electrolyte problems and dehydration which could be serious.
Acid reduction meds. Reflux may be the problem andtreatment with a proton pump- inhibitor, Pepcid or Prevacid (lansoprazole) may be of help.Try the medfor a week and report back to your pediatrician with the results.
See a doctor. This is an urgent issue. There are a number of causes of what you describe, and most of them are serious enough to warrant an urgent visit to a physician. I hope they are better soon.