What happens if a girl tells you that she wants nothing for valetines day?

It depends on how long you have been together. If its been a short time, she may not want to make you feel obligated so early in the relationship. If you have been together a long time, she may know you don't have the money or she doesn't want you to think you still have to prove your love that way. It could also mean she is going to break up with you and doesn't want you to buy her a gift because she no longer wants tokens from you. There is also the possibility that she just doesn't like receiving gifts.

The best advice I can give is to ask her what it means, the key to any relationship is communication. Good Luck :)