Does an employer have to abide by doctors notes?

No, they do not automatically have to abide by that: the doctor is not a school district official or member of the board of education, and so has no power to directly order the school what to do. She can request it as a "reasonable accommodation," but that is not the same thing as saying that the school *must* abide by the instructions; rather, if she has medical documentation that she is allergic to mold and there is some reasonable basis (some evidence; more than a mere "suspicion") to think that her classroom has mold, the school must consider moving her. However, while considering it, they are allowed to take into account not just the evidence of her allergy and the evidence of the mold (they do not need to act without evidence), but also whether they can move her without unreasonable cost or disruption. It would be one thing, for example, if they have a spare or unused classroom that is in usable shape--moving her and her class then is not a problem. But if there are no classrooms to move her class to (all are in use) and if moving *her* to teach a different class would be disruptive to not just her class but the other class (because they'd have to get used to new teachers; the teachers may not be fully prepared for those other classes; it is not easy always to pick upon someone else's lesson plan; etc.) then they would not have  do this--they would not have to, for example, disrupt the education of 40 - 60 students in two classrooms to accommodate the suspected impact of mold on one teacher.