Mystery's "You've Hijacked My Brain" routine is probably your best strategy. I suggest you get something for her. Nothing big, and nothing plastered with "I Love You"s. Like, a small stuffed animal or a single flower (not red- research the meanings of roses before buying). Something homemade is even better. Shoot, make her food or something. Or a card. Make her a card- don't buy it.
One small gift is plenty. Just something to say, "thinking of you." I would give it to her and say something like:
"I was in the store this week and I passed by all those Valentine's Day decorations. I couldn't help but thinking of you when I saw them. You've been on my mind a lot this week for some reason, so I figured I would give you a little something to tell you that I'm thinking of you. Now please get out of my head

"