Definitely involve admin at this point. Last year I had one of my DDs removed from her math class because the teacher was obviously picking on her. The AP said "I don't see how their relationship can be repaired" after I showed her communications I'd had from the teacher, and told her some of things DD said about the teacher ("she hates me, she thinks I'm stupid.") And while I'm sure the teacher didn't actually hate her, it was clear she strongly disliked my DD.
As for the bathroom thing, I do think it's disruptive. I'm sure he's doing it as a release, but that means he's most likely asking to go when the stakes are highest. For example, she'll start test instructions, but he has to go to the bathroom which is a disruptive. I think she needs to think outside the box a little bit and say "before I give test instructions, please take this time to go to the restroom". Or like PP said "for the next 10 minutes no one can go to the bathroom." BTW, does he go that often at home?
And in regards to her asking him if he needs to go to the doctor, I do not for a second believe it was said with kindness and concern from him. I don't think she should have said anything to him, *a child*, even if she was concerned for his health. Like he's supposed to make his own doctor's appointment? Or if he has a diagnosis he'll be the most reliable narrator of what that is? I doubt she pulled him aside and said gently "DS, is there a medical condition that I need to know about?" More likely it was "maybe you need to go to the doctor, you go to the bathroom too much" said in a snarky way.