Sadie is correct in that everyone takes different times to get over breakups. You can't use the length of time you took to judge how long it takes someone else. It is similar to grieving in that way.
However, there may be more to it than she is letting on. She may be saying she isn't over her ex as a way to let you know that she isn't interested in pursuing something further with you. I know that sounds harsh, but a lot of people would rather avoid a conflict by saying something they think will stop the pursuit.
My suggestion is to remain friends with her, but not put all your eggs in one basket. Don't keep yourself from becoming interested in anyone else because of a maybe-down-the-line thing.
Brought to you by Dating With Devon!