I think what bookwormde was saying is going to be the problem here.
The child can't be expelled for behavior related to a disability- well they
can but it is quite a process- but the problem she has is that the child doesn't have an IEP already in place. In other words, the school has not formally recognized a disability (whether the child has already been in therapy and they should know about it or not, they personally haven't acknowledged it exists, therefore it does not exist)

, so they are not required to treat her differently than a typical kid.
I believe the next step of the process (besides getting an advocate) would be for her to request testing, which they would have to do within 60 days. (that's calendar days, not school days) The law says that the child stays with their current placement until testing is completed and an IEP is written. During that process, they will request copies of her medical info, so they will be officially told of her diagnosis. If she does not agree with the school's conclusions, she can request independent evals. She's going to want an advocate the whole time so they know she's serious, and everything in writing. If it's not in writing, it didn't happen.
The real question is, how much of a fight does she want to take on? I'm not advocating walking away, but she should be aware of what she's walking into. It looks at this point that she's got two options- one is to get the attorney, throw a fit, prevail, and then send her daughter to a school where she (the mom) has pissed off everyone there and they don't want to deal with her and her kid might as well have a big flashing sign over her head every day... or two, get the heck out of there, let them "win", and find a place where her daughter will be treated fairly. It's a sad choice, but not that rare, unfortunately. I mean, I'd fight it too, but she has to know there can be a cost.