Cook her a nice dinner in front of her -- something fancy but not too difficult or expensive. Lots of webites with easy stuff to do. It doesn't gotta be a lot of work, trust me.
BTW, if you don't know how, start learning now, not the night before. It ain't hard to do if I can do it but planning is everything.
Upside is her reaction will be, "Wow, you did this for me!?!"
Downside is if she finds out you were going to and then didn't, her reaction will be, "So, I'm not worth the effort!?!"
The rewards can be mindboggling, however. Women dig guys that can really cook. And if it looks easy, it probably is easy, but do not, repeat, do not tell them that. Be humble with your great skill and monstrous talent.