Only she knows why. Why don't you just ask her? If you two were/are really friends she should be able to give you a direct answer if you aren't too weird about it. Generally, tho, friends who develop feelings for each other, whether its one or both, are in for trouble by trying to stay 'just friends'. Usually, its a big fat lie for either one person or both.
I agree with Juristhea: sometimes a gal will cut off contact with a guy if she has feelings for him & doesn't want to.
Or mbe she thinks you won't move on & find someone else to date if she doesn't cut you off. Again, only she will know for sure. So go ahead and ask.
Second thoughts can generally be amended with judicious action; injudicious actions can seldom be recovered with second thoughts.
--Cyteen by C.J.Cherryh