Lies

I am facing a big problems here. One of my friends lied to me. I am thinking of forgiving her or not.

Any suggestion? My friend been lying me something. When I asked her something, she said that she didn't do it. Which means that she was not admitting it. But now I figured out this myself, and I feel being fool.

I don't know whether I should forgive her or not. What I think is I just can't believe that she will lie to me since I tell her everything. This feeling is really not very good...

T_T