I’m generally quite uncomfortable with training sessions where I might be expected to do things I haven’t mentally prepared for. Indeed I walked out of a work event a couple of weeks ago, because I was prepared for lectures and panel discussions, where audience input would normally be in the form of voluntary questions, and instead was being asked to do various verbal exercises with a stranger who happened to be sitting beside me.
So I can imagine a situation where B thought they were going to have reasonable adjustments explained to them, and instead found themselves having to participate. So it does rather depend whether B is someone who genuinely needs reasonable adjustments herself, or is just an awkward sod.
Am I correct in thinking that reasonable adjustments, in the normal way of things, would be agreed between the manager and employee, and then introduced to the rest as something that the manager had agreed to, and was therefore more official? Presumably other people could then object to management directly if they disagreed? Any attack on the employee themselves or failure to comply with the adjustments would also be for management to deal with.
But if this was a trainer, I would expect her to be able to train people and, to an extent, that should involve being able to deal with difficult trainees.
It does sound like B was beyond reasonable and the trainer would be within her rights to ask B to leave the session and explain to the manager(s) who brought her in, why she had done so. I would then expect the manager(s)to talk to B about it, to hear B’s side, and find out why she behaved so badly.
Only after hearing B’s side, and ideally also after hearing other people’s comments about what occurred between A and B, would I then be able to make an assessment of who was unreasonable. It sounds like B, but it’s always important to give people a chance to explain themselves, even if you have to take past behaviour into account.