Some teachers (by no means all or even most) seem to have issues w/special needs kids. They express that "it's not fair to the other kids, they don't get such and such". Ask her if a child wore glasses, needed glasses to do their work and learn, would she take the glasses away because the other children didn't need glasses and "it's not fair!"? Unless she's really nuts, she'll allow as how not all kids need glasses, but those that do really do.
It's the same principle w/the supplies you're talking about. The other students don't need those supplies, your client does. If the location you're using is inconvenient for her, negotiate an acceptable alternative--be as flexible as possible!
Whatever is the basic diagnosis for the child is, google it and print out a simple explanation for her to keep. The kid probably has an IEP, you should be sitting in on those meetings and ask for provisions in the IEP that enable you to give the care you need. If that isn't possible, tell mom what you need and perhaps she can get it included in the IEP. Once it's in the IEP, it's much harder to not do it (because IEP's are legal documents, the school is bound to provide what's on them).
If there is a school nurse @ the site, try to communicate w/her what's going on w/the kid--she may be able to help you when conflicts arise.
If there is a condition change that means the child needs to go home, follow the normal proceedure for taking a kid out of school. Mom calls the office, office calls the teacher, etc. Schools like their proceedures followed and everyone gets bent out of shape when it doesn't happen. Nurses tend to think "patient first" and just go, but it will pay you back if, barring a life threatening emergency, you follow the directions.
I'm the mother of a former "spec ed" student, I once told the psychologist that it wasn't my goal to be the mother from [heck], but I was more than willing to go there if necessary!
I hope you can work it out--make it easier for the child AND, of course, you!!