PPS- If the pain is located at the bellybutton, or down to HER right of it , please take her in. Could be appendix. usually has fever, vomiting or nausea and bad ache in that area.
Sound like a virus. If it continues for more than today, I would take her in to make sure. Or if she gets a fever over 101 or has pain, take her in.
Try giving her warm water to drink. As hot as she can stand it without burning her mouth.
It will help the esophagus muscles and tummy muscles relax so that the vomiting stops. It also clears the tummy of bacteria or virus. Sip it if she is still vomiting. If not vomiting, drink it like a reg cup of tea.
If she gets nauseas, you can buy what is called anti-nausea liquid at Longs Drugs. It is merely coke syrup. Yes,....coca cola syrup....no fizz. Resolves nausea instantly and very safe!
If you can't find it, call around to the drive ins and see if any one will sell you just the syrup. McDonald's here for us does.
It also stops vomiting in small doses.
Best of luck. Will pray for her.
PS-Undigested food is pretty normal with a stomach bug. Stomach rejects it due to illness so it comes back up.