Hi Steph,
The juices of fruits and vegetables are higher in oxalates than the whole food, but the fiber in the fruits and vegetables helps to remove the oxalates. By any chance, is your daughter drinking a lot of juice, but not consuming the whole fruit and/or vegetable? If so, cut out the juice and insist upon the whole food. Failing that, get her to drink a glass or two of citrucel or metimucil every day, and see if that has any effect on the oxalate levels.
Food that are particularly high in oxalic acid (oxalate) include sorrel, rhubarb, and buckwheat, as well as black pepper, parsley, poppy seed, amaranth, spinach, chard, beets, cocoa, chocolate, most nuts, most berries, and beans. Clearly, cutting out all of these foods could have a major impact on your daughter's diet. Given this list and your daughter's other dietary restrictions, look for recipes (you can find a lot online) designed for a celiac diet and adjust accordingly. My adult son has Crohn's disease and must also keep a gluten free diet, and for a while needed to maintain a dairy-free diet as well. He makes pretty much everything from scratch as gluten and dairy pop up in most processed foods. He uses a home made gluten-free flour for anything that requires wheat, and it bakes up pretty well. He (and I) have used it to bake breads, muffins, pies, cakes, and for breadings that are virtually indistinguishable from wheat-based products:
6 cups rice flour
2 cups potato starch
1 cup tapioca flour
2 tablespoons xanthan gum
For a sweeter flour, substitute 1 - 2 cups of the rice flour for sweet rice flour. Considering your daughter's hyperoxalemia, I would avoid ready-made flours and breads, as many use bean flours. As far as dairy substitutes, hemp milk, soy milk, and rice milk work quite well. I would avoid nut milks and nut butters, though. I also suggest you get a referral for a competent nutritionist. Check with UC San Diego to see if they have a doctoral program in nutrition, and if there is anyone on staff at their medical school who you can make an appointment with. A couple of years after our son was diagnosed, we were able to have him evaluated by a prominent doctor and his team at Columbia University in NY. The team included a nutritionist RN and a PhD nutritionist, and their input has been invaluable to his treatment.
Good luck!