I feel so bad for you and your kiddo

. GI problems are so frustrating to get to the bottom of.
This will sound simple, but one thing I'd do is get her on some probiotics...maybe do Benebac paste for 4-5 days, and then switch to the powder after that. Especially w/ GI issues, the small intestine gets really an imbalanced flora and giving probios for a good 6 mths can really help.
It does sound kind of IBD-ish and I hope you get a definitive answer soon.