What we do?

She is my good friend but...

Please clarify your question

How old are you?

To answer your very vague question... a friendship with a girl (assuming you are a guy):

"Whether or not a guy and a girl can be just friends depends on how the friendship started, on whether or not there is a physical attraction involved, and on the personalities of the individuals." (About.com)

"Rules for a Successful Guy-Girl Friendship
There are some simple rules to make a guy-girl friendship a success:

* don't ever cross the line of friendship without realizing it may be a point of no return

* if you know your friend has feelings for you never take advantage of those feelings

* never give in to physical attractions without knowing that it could change the friendship forever

* know that there will always be people who scoff at the validity of guy-girl friendships

You can be friends with anybody you want. Gender is not a deciding factor. If you meet somebody and like them as a person don't let something as small as their sex keep you from being friends. Good friends are very hard to find. " (About.com : Teens)