First, it is not easy to judge a person as an apostate. You have to be knowledgeable enough to know what constitutes apostasy and what does not.
Second, supposing that she has really become an apostate, you should not have severed your relation with her. Of course, you have to show her your disapproval and total rejection of what she did. This has to be manifest in your attitude toward her. But at the same time you should keep ties with her in order to advise and help her so that she may come back again to Islam. You should use any contact with her to attempt to discuss with her her problems with Islam. You can provide her with books, tapes or internet sites that help her have a clear vision of Islam and answer her doubts.