For the stomach issues, perhaps see if you can get into a gastroenterologist. An academic center like Mayo or a university could be a good option for any of the specialties.

Prepare for the appointment. Collect relevant information. Have your daughter keep a symptom log, describe the impact of the symptoms (how they affect her daily life), collect family history information. Try writing down your questions ahead of time. I find this pain scale helpful because it includes descriptions (https://myhealth.alberta.ca/Health/pages/conditions.aspx;). I bring a printout with me to doctors' appointments. Sharing it helps me establish a common framework with the doctors.

If you are in the US and if your means allow, perhaps order some blood tests for your daughter on your own through LabCorp or QuestDiagnostics. Here are some resources from LabCorp (simply because I used them myself). I started with Rheumatoid Arthritis as a topic because many of these tests will overlap with "related" diseases. This page lists several relevant tests: Our Guide to RA testing: Rheumatoid Arthritis https://www.labcorp.com/treatment-areas/rheumatology/conditions/rheumatoid-arthritis

PS: There is a neuro-gastroenterologist on Instagram (https://www.instagram.com/drzacspiritos/) who talks about some of this. His content seems sound.