Most of what I have to say about the situation with Ali's aide has already been mentioned, but with the information from Leah's instragram posts taken into account, it sounds like there was a temporary staff issue that was that was either explained incorrectly by the principal, or misinterpreted by Leah. All respect to principals, but many building administrators do not actually know a ton about special ed and can have trouble understanding or explaining things to parents, especially with legal stuff. It should really have been something that a special ed administrator or Ali's case manager should have contacted Leah and Corey about immediately.
I hope that my guess on that is right - I was very upset initially thinking that the school was actually trying to put one over on them, but it's also not news to any of us that Leah and Corey have not necessarily done a great job of informing themselves and getting involved with parent groups, etc. At least Corey pointed out right away that they can't just change the IEP without a meeting, but it was interesting to see Kail suggest that Leah get involved with some parent groups for kids with MD and that seem to be something she hadn't really considered before. Their (understandable to a point) denial of Ali's needs is not doing them any favors when it comes to knowing her rights as a student with a disability and the channels to go through if something like this comes up. Ali has a case manager they could contact, and either her school or in the district there would be a school psychologist and an administrator in charge of special ed. Unless editing left out them talking about contacting one of those people, that's them not doing their due diligence. The school is responsible for implementing the IEP as written and making sure her parents understand the process, but they also need to take initiative to talk to the people in charge of special ed if they think something is not being done right. Worst case scenario if the school is actually being shady or out of compliance, sometimes just threatening to request a meeting with attorneys present is enough to straighten things out (plus Leah has the leverage of being on TV as well). Joining parent groups wouldn't only benefit them by helping learn more about MD - it would also help them know about access to parent advocates to bring to meetings, etc.