I know that you're feeling VERY upset over your son's distress-- that's completely natural.
I would still advise you to go into the meeting with an open mind, though--
and remember-- until you HAVE an IEP/504 plan, accommodations are sort of a grey area. This
will be a short-lived phase, one hopes.
You never know-- maybe your DS' account IS missing some salient features that just don't occur to children in the moment. At least she responded quickly and
cordially to you. That part of things, at least, feels quite professional. So my advice is-- wait and see what she says. Let her talk while you listen first, then decide what to do with what she tells you.
Listening obligates you to nothing, after all. I might hold off on a call to the psych until you talk to the teacher-- either way, you'll know more about what you'd like to cover.
Good luck!!
I hope that it turns out to be a series of misunderstandings and the lack of a 504 plan in place.