This was a spectacular failure primarily, I think, on the part of the administration. My knowledge of special needs and IEPs is pretty limited, but it's my understanding that an IEP is developed and monitored by multiple parties, including someone with expertise such as a school counselor, therapist, or social worker. Heck, my DH is a football coach and he needs to be aware of IEPs for the students he coaches. The administration repeatedly telling the OP to just work it out with the teacher, while not providing the teacher with the necessary training or consulting with an expert, is just bizarrely irresponsible.
I disagree with the posters who are saying that the OP did everything she could to advocate for her child. Unless there is something left out of the story, she let this mistreatment go on for a year and never looked outside the school's administration for a solution. Personally, my first step would have been to get my child's therapist involved. If that didn't work, a lawyer. I would have escalated to the county's administrators, the school board, possibly even the media, whatever was necessary. The teacher was certainly in the wrong, but she was also thrown into a situation for which she was unqualified and clearly in over her head with no support whatsoever. I think the OP's focus on the teacher as the main source of the problem, while understandable, was misguided.
That said, I don't think the OP owes the teacher an apology. She didn't go on a expletive-laden rant or throw a fit; she became emotional and accused the teacher of something she believed to be true -- after the teacher had refused to accommodate the child's IEP for a year and stated that she would continue to do so. If that's not provocation, I don't know what is. She was interacting with the teacher as a parent, not as a professional colleague, and parents shouldn't be expected to put aside their emotions and act professionally under those circumstances.