Run in with my ex-girlfriend?

Hello all, I found out that my Ex-girlfriend and I are going to be in the same place at the same time at an event coming up. We didn’t have a bad break up, and we still exchange emails from time to time, but nothing overly friendly. We haven’t seen each other since we split up about 8 months ago. I know she is hanging out/dating a guy who may or may not be with her at this event. I’ve lost about 25lbs of fat and put on a good deal of muscle since the last time she saw me, so I look different now. I’m just wondering how to act if we end up running into one another. I wouldn’t mind talking to her and being friendly to her and her new guy if he's with her. Also I wouldn’t mind her seeing that I’m in great shape now and doing much better for myself. I just don’t know if I should approach her if her new guy is with her and introduce myself or what? Or wait till I can catch her alone for a minute? I don’t care that she’s seeing someone. I have nothing but the best wishes for her, and hope she’s happy. I’ve never been in a situation like this before, and since I haven’t seen her in so long I would like to be friendly. How should I approach the situation? Is there anything in particular I could say to her to maybe spark her curiousty or interest without stepping on her new guys toes?