That was the first thing that I thought when I read the thread title, never mind the first post!
Depending on the age and ability of your girls, you could try the lovehearts game? Everyone gets one of the loveheart sweets and you try to tell a story, with each person incorporating what their sweet says into the next part of the story. It can get quite ridiculous.
If I think of anything else, I'll let you know - we've never played Valentine's themed games at Brownies!