Some ways to let her down easy...
1. Take a shower with her...and start peeing. On her. But make sure she's watching (i.e. not when she's shampooing and got her eyes closed, although I'm sure she'll smell it).
2. Let her 'accidentally' catch you wearing her thong underwear. Give it back to her dirty, like after a night of Indian food.
3. Tell her that you've discovered something called a 'donkey punch' and that you'd like to try it with her. Explain the procedure in detail. (Don't actually DO it for goodness sakes! Not even as a joke!)
If she is alright with all of these things, she's either the coolest chick in the world and you've hit the motherlode, or you should just run because she's obviously insane.