The same thing happened to me. The week before school started I emailed DS's first grade teacher and said briefly that he is "unusual", we had a neuropsych eval done the previous spring, he has an IEP, he had a TBI, etc. I wanted to have a casual conversation with the new teacher about his recent history and come up with some sort of tentative plan on how to deal with him. Next thing I know I get an email from her stating that she invited the IEP manager to join us as well as the OT and principal. I had a 1-day notice. So what was intended to be a casual meeting for me to introduce myself and DS, turned into an IEP meeting, complete with the form for everyone to sign. Considering I had major concerns about his IEP and how they had handled things the previous year, that did not make me happy. The IEP manager was probably trying to make sure I had no opportunity to talk to the teacher privately (I think she found out and basically invited herself). So much for being able to talk freely to the teacher about my concerns!
For the latest IEP meeting where they were going to go through eval results, I specifically asked that they give me a report of results ahead of time. I got half of them but not the other half. So I had to listen to a play-by-play of the assessment from the adapted PE teacher of DS and his clumsiness (it was almost comical) while 10 people watched me take it all in.
I think it is within your right to ask what is going to be talked about at this conference and who will be there. If you feel uncomfortable with it, tell her that you would prefer to meet privately for the conference and you can schedule another meeting if other people have information to share.
