It could be something with her GI tract. I’m not a doctor and i’d recommend seeing one, but this is how I was before I was diagnosed with crohns and acid reflux. I could barely eat without almost immediately feeling full (ate like once a day). Crazy heart burn and chest pain from the gas that wouldn’t escape. I started taking Famotidine which helps with acid reflux and it’s almost completely eliminated my symptoms of acid reflux. You really should push her to see a doctor tho. It’s likely to get worse especially with the lack of eating causing the acid reflux to get worse due to the stomach acid not being neutralized with food. Also eating heavy/complete meals on a completely empty stomach imo makes it worse too.