I completely understand your situation. I've looked at many food lists for FPIES kiddos looking for ideas, and they all seem completely different. Every child is unique- it really is all about food trialing very carefully. I found it best to avoid the common triggers as most of them were a problem for my son, but that isn't always true either (My son can tolerate peas which is on that list. And it looks like your daughter can tolerate rice and sweet potatoes.).
I can speak personally about your formula dilemma. Have you tried Elecare? It is an elemental formula similar to Neocate, but tastes better. Some FPIES kiddos found success with it.
My son happens to react to Elecare, so we had the Neocate battle as you described (mixed it with everything including breastmilk) and complete refusal to drink it- We tried for 2-3 months and then we gave up. At one year of age, your child can try Neocate Splash. My son LOVED it and tolerated it! : ) (We actually didn't discover this option until my son was 3- I breastfed that long. Our dietitians were and continue to be unhelpful.)
Don't worry about being proactive about trialing foods. We made that mistake and did too many food trials early on- My son just ended up being sick a lot. We currently trial about once a month and/or easy trials when busy (different way of cooking the same food). We only do high risk trials in the summer, since viruses mess with everything. We are all much happier as a result.
Hope that offered you some practical advice. Best wishes!