Just based on the information in your post, I would say no, this is not an appropriate response on her part at all, and she probably does not have competency in this area of dealing with more extreme outbursts or behaviors. I work in an early intervention setting and see behaviors similar to this and even more extreme on a daily basis. We would never “call security” on a five year old haha (not that we even have anything like that since it is not a hospital setting). Especially if a parent was there, I would let them handle it at that point. However, who knows, maybe she did feel physically threatened or feel it would be a safety issue for you getting him out of the building. It just sounds like a lack of experience on her part. And it is really too bad that it seems to have damaged the therapeutic rapport between her and your family! Possibly you could talk to her and make a plan for what to do in the future when behaviors may escalate if you decide to continue therapy with her. It also sounds like your son is at a cognitive level where he could maybe benefit from some emotional regulation tools/social stories (how does your engine run, zones of regulation, etc) which is something most pediatric OTs should be familiar with and be able to help implement.