Wow! Your poor child! My heart goes out to you.
Do you have a good naturopath who specializes in stomach disorders? A LOT (in fact MOST) of the time when a person has GERD, they have too LITTLE stomach acid. (I had it for a couple of years, and also when I was pregnant). If it wen't for digestive enzymes, I would still be terribly sick. These medications such as Prilosec and Zantac inhibit the absorption of vitamins, and a lot of drugs are untested on children so they don't know what effect it will have down the road.
The reason you can get acid reflux with too LITTLE acid is, the food gets old, it starts to develop gas, because it can't go "down the chute" and it backs up into the esophagus.
There is one good test to see whether or not this child has too little or too much stomach acid. Feed them a tablespoon of either lemon juice or Vinegar. If they feel better, they have too LITTLE acid. If they are worse, they have too much. My sister had GERD and I asked her to try this, and it wiped out her symptoms in about 2 hours. Believe me, she did not want to swallow vinegar, but the results were amazing. She started commenting how much better she felt. That's probably why those medications aren't effective. It's the opposite of what your daughter needs. My kids love to have lemon juice in their water (without sugar) because they learned from Mom that she puts lemon in her water.
I also discovered Naturopaths have tests for food allergies that MDs don't have. It's worth the cost, I'll tell you. They have saved my life, and me from Chronic Fatigue, which I had for 12 years.
God bless!