Terrible idea.Id start with her phone. Get that fucker when she is sleeping and check it out if its not password locked, which could be another sign.
You guys are all fire and brimstone. Relax. Not every girl is a mindless skank who is constantly on the prowl for a better dick. Maybe she realized she spent her entire youth with one guys and is starting to wonder if that's all there is? Maybe that's why our man doesn't care much either? Just give her space and treat it as a breakup, doing your own thing, seeing other women, etc. If she decides she wants to get back together, and you do to, think about it. No need to demonize every chick in this thread.
P.S. I'm not planning on asking out hair stylist chick. Was just curious.