Turns out she is ok, no appendicitis. Thankfully. The tests were rough, especially for her. We ended up having to sedate her so she could get a CT scan, which I was very much against but there's that urgency. She's sleeping it off at home right now. Looks like it was just some kind of virus that caused some extreme stomach pain.
Before we took her into the Dr I was talking with my wife about this, how in a kid with her kind of condition (ADHD, sensory issues, possibly bipolar) it's hard to really gauge how serious things are. Like, was she really in that much pain? Who knows? She's come up with ways to handle the other sensory issues, like wearing ear muffs to dull sounds of loud groups or movies or whatever, wearing long sleeves/layers to cover up from heat/cold. But with pain, she just can't handle shit. It's like the world's worst super power.