What does her period have to do with any of this? Do what you usually will do on any given Valentines day. Buy her some stuff. Stuff is always good. Then eat her stuff.

Dude, you're totally killing the spontaneity of anything that might happen, and therefor the PASSION as well. Instead of asking people what they think you should do, why dont you just let it happen. Build off the passion of the moment, rather than some plan you came up with. And nothing says you can't eat her out while she's on her period..