I think you may be over-reacting slightly. I’ve done some tantric yoga and it was just a bunch of breathing exercises, nothing all that sexy! 🙂

I think the suggestion of going with her is a good one. It will give you some idea of what she’s doing and you can talk about what she enjoys about it and help calm your fears a little. Or, if it does feel a bit sleazy and too free-lovey for your tastes, then you can talk to her about that and point out specific things that people said or whatever it was that rubbed you the wrong way. An informed conversation is generally a good idea.

Good luck!