My daughter had a similar complaint. In her case, and it may not apply to you, she had insufficient stomach acid. She was told to take some apple cider vinegar before eating and that did the trick. When people suffer indigestion they assume it is from too much acid, but more often than not, it is the lack of acid. Anyway if she tries the apple cider vinegar and it does not improve her situation, it will do no harm. She should try one teaspoon for starters. My daughter found she needed one tablespoon. The doctor said that that was fine.
i had that yellow stuff coming up. i had a camera put in through my mouth into my stomache which said i had a hiatis hernina. the yellow sore tasting liquid is acid which comes from the stomace. tell your friend to eaat her last meal 3-4 hours before bed time, sleep on a high pillow and aviod all acidy foods, eg, lemon, orange etc... my gp has put me on omeprazole. it has helped me greatly
When I vomited yellow/green though it was just two days I went to hospital and found out that my appendix was gangrene and perforated and had to be removed. She may not have the same problem but she needs to go to a doctor.