Honestly...she had her tits out, so what. We need to start remembering that we are not in CONTROL of our partners for 1 and for 2 if she were a man this wouldn't bother you. It's just some nipples bro. If you don't trust her then that is something you need to work on. Imagine had you reacted positively to the picture, because it sounds like it was funny, she would probably me more open with you. She also doesn't HAVE to be ready to move in together just because you are or just because the relationship is however many years long. She'll be ready when she's ready, if that's a compromise you can't make then it's up to YOU to deal with that.
Just remember you are two separate people with two separate lives, even if you were living together, would you rather her feel like she can be herself and open with you or like she has to hide parts of herself?