I'd say NTA. However if she behaved in the manners you suggested early on, you could also say that her attitude was likely also simply put juvenile. Part of me wants to say subconsciously you also saw this and wanted an unbiased opinion of her behavior (a gathering of co-workers would due of course) and after seeing their reaction you could confirm that she was unable to maintain a mature attitude and was frankly incompatible for you (which is all well and good and you're not the asshole for realizing you weren't happy and moving on)

However from a different view point (devil's advocate here) it is possible that she could tell that you were tense/uneasy and simply wanted to make you/the room laugh to lighten the mood, however I will agree that if things occurred as you said that was certainly not a proper way of going about doing so and I go back to refering to a juvenile attitude.

I would say there is a slight bit of assholery on your end, simply for your co-workers having to be put in that situation. My only bit of advice that I could give would be: there's nothing wrong with having fun and filling your time with the company of another; however identify infatuation vs actual compatibility before involving friends/family/co-workers in your relationship (that way you don't have anything to explain or justify afterwards)