I'd give her the teddy bear at work and give her a card (Hallmark not Wal Mart) that has something saying "Be My Valentine". Ever since we were little kids we've always said to Grandma, Granddad, dad, your best friend "Be My Valentine" so I don't think it would sound creepy. I like telling her that you won the bear for her because it shows that you have good luck, you're a winner, and you thought of her immediately! Plus it may make her think about how many times you tried to win it just to give it to her! Determination.... women love to be pursued.
Gifts at work are brownie points!