I would find that really weird as well. I worry sometimes when I've gone along to an interest or hobby group that my T will be there. One time a T I only saw for one session was at a class, but I don't think she remembered me as it was some years later. Still felt weird though. If my current T was at anything I think I'd have to walk out, it would feel really awful to me.

It sounds to me like your T handled it like a pro - she didn't ignore you or act uncomfortable with you both being there. And good that she's open to discussing your feelings about it.