Hard NTA. Myself, and a fair number of my friends are what you would call gym junkies and, at least in our cases, we all know or have some idea if our tights are getting a bit thin and therefore potentially see-thru. Guess what? When in that situation we either don't wear the tights anymore, or get one of our friends to check (yes while doing squats) if it's ok or not. She wanted attention otherwise she wouldn't have been wearing something borderline. There are also so many training aps, workouts, plus people filming themself for technique or training purposes its never crossed my mind thst someone is filming me just because they have thrir phone out on the gym floor. And to come at you while filming is just another level, I agree with the person who advised you to keep an eye out for her video on social media so you know who to sue. I would have told HER to stop recording me immediately.