The herb agrimony is beneficial for people with malabsorption. It is safe for children.
Purchase dried agrimony, and make a herbal tea for her to drink before each meal. Make it in advance so it is cool enough when she drinks it.
Even while doing this, still be careful with the diet. You may experiment with small amounts of risky foods, and see if she gets a reaction to them. If she does not get a reaction, try increasing the amount a little each time.