r u actually dating and seeing each other during the course of your 6-month relationnship? or just talking on the phone? Is this a long distance relationship?
well, if you are going to get married and are( although i did not get a clear answer to this from your post) just involved in a long distance relationship i hope that you will get to know each other first. women can be very sexual. it's just not as widely discussed as men. and as for the phone sex....well, if she is a virgin she is living in fantasy and that is exactly what phone sex is... yes it is possible for a virgin, especially one with a vivid imagination.
i just don't think she has been having sex with her relative. if she is doing the real thing then she probably would not want to fantasize about it quite so much.
as for telling if she is a virgin or not, i'm not sure. most but not all women do have a bit of bleeding after the hymen is broken, but the hymen can be broken from non sexual occasions as well.