If you are planning to get married, then you should get married now before her visa expires and then file for her permanent residence on the basis of the marriage. Once her visa expires, you will still be able to do this but this is going to be the only way that she will be able to legalize her status once she becomes unlawfully present at the expiration of her I-94 and she will be subject to removal.
Answered on Sep 20th, 2012 at 2:56 PM