Forget about eating out. Not going to happen on Valentine's Day. Everything is going to be booked up.
Cooking your own dinner is a good idea. Another idea is to eat out the night before and save the leftovers for Saturday. Let her pick the movie you're going to go see or rent.
If you cook your own, you can't go wrong with a chicken dish (she might be on a diet or be a semi-veggie gal). Go pick up a package of chicken breasts or chicken cutlets (whichever has the least amount of fat marbling), some mashed pototoes (or stuffing), and Birdseye green beans with roasted almonds. Get some BBQ sauce if you don't already have some, and maybe a small loaf of deli bread. Trim the fat from the chicken, then pan-cook the chicken (cover with the lid to seal in the juices and heat) and follow the instructions on the box for the taters/stuffing and beans. I prefer to put the sauce in a small dish and dip the chicken - you two can share the sauce that way. Girls dig sharing.
Serve wine if she's up for it. Otherwise, cold apple juice makes a good compliment to the dish.