Blood in stomach

So we've had a few days now where C has been gagging alot and coughing up lots of mucous and phlegm. It gets worse in the afternoons as she gets tired, and is particularly bad whenever she has to lay on her back - like for changing diapers or clothes. On Wednesday afternoon (2/4) she gagged and spit up a large amount and the emesis was dark brown. We checked the residual in her stomach and drew out lots of dark brown liquid. It is not unusual for C to have streaks or brown gobs in her residual, and I normally associate it with her needing to have a BM. This was different - the entire stomach contents was dark brown. Nurse says it is most likely blood, so the question is where is it coming from. We know C has a history of gastritis from stomach acids irritating her esophagus and it could be she is having a flare up of the inflamation. We did not rush to the doctor, but took a wait and see approach. The brown residual was gone by 7pm. Overnight she slept OK but seemed to be grinding her teeth a lot. Yesterday morning when we got her up for school and checked residual it was brown again and she again was having lots of gagging. The school nurse called in the afternoon to say C was drooling excessivley, gagging alot, and just not herself - even whimpering a few times. They vented her g-tube and drew out lots of frothy mucous. I went to pick her up rather than chance her throwing up on the bus. At home I checked residual and there was no blood. She had a decent afternoon, was happy and enganged with the nurse. Lots of drooling, tongue thrusting, and some gagging but not excessive. So as of this morning she is back at school. Residual is still clear of blood. There are so many things that could be bothering her. Perhaps she has a sore throat (although nurse said her throat looks OK). We know some 12-year molars are coming in and perhaps they are bothering her. Or one of her recent spit ups caused the inflamation in her esophagus to flare up. Probably all of these things. But she's not in obvious pain and as long as the brown/blood goes away, I'm not too worried. Will keep the Dr. Sahgal appointment today for Botox and perhaps another baclofen adjustment.