Why did just the feeding tube stop the vomiting?

[Feedingtubesolution]

My daughter is 17. She has a number of health conditions: Bipolar, PTSD, asthma, and migraines. She also suffered a severe concussion 2 years ago. It took months for her to be able to pass the concussion test.
In August, she started vomiting daily, up to 7 times a day. Her pcp tried some medicine and referred her to a GI specialist. She was down to 104 lbs (5'3") from 112. An upper GI suggested possible SMA. (She had no pain at all) They were going to scope and place an NG tube. They placed the NG and didn't scope. Ugh! Anyway, the vomiting stopped as soon as the tube was placed. She had it for 2 months. After it was removed, the vomiting returned. A scope revealed thrush completely coating her esophagus. (Perhaps from her ADVAIR inhaler?). She was given antifungal meds for 21 days. (Again she had no pain.) She had intermittent vomiting. Now she has finished the medicine and the vomiting is back in full force. She is back down to 107 pounds from 111.
We are waiting to see the GI again.
Questions: Since she had thrush before the NG, why did that stop the vomiting? Could it be something spasming that the tube stopped? If she did have SMA and thrush, why didn't she have pain? Could this all be related to her concussion? I have yet to convince a dr to do an MRI even though her migraines have become intense and she is having memory and cognitive issues. Thoughts??