You have to let her know what you think in you mind. If not, she may think you're just in bad mood for the day and will play with her again on another day.
If you don't want to tell her directly, you can use electronic means. For examples, send an e-mail, a SMS message or a MSN offline message to express what you feel and the reason. It's important to show you're serious and let her to have rooms to improve. Otherwise, she may just think you are not fair to her and make the problem be more complicated.