Slip two quarters in an envelope on her pillow with the note "call for help any time" and let her go. Unless she is bumming at a friend's, she'll be back within a few weeks. You may want to consider providing her some kind of long-term birth control if she is not responsible herself- hormone implants, IUD or whatever works. Stay out of her business. As much as she may hate you for knowing anything, it will worry her if you ignore her.