You are right to be concerned, the Brahma Kumaris goal, or if you really wish, the goal of the "spirit entity" which speaks through the BKWSU's spiritual mediums and guides the religion, will be to either draw you both in or separate your partner from you and her family and, basically, brainwash her into believing in their religion using a fairly hypnotic trance meditation. I have sent you a private message.
We can help you by outlining what they will be telling her and what their ultimate teachings are. If you are interested, we can even show you one of their teachers' manuals, here:
Teacher Training Manual.
For susceptible individuals, being sucked into the BKWSU can be very pleasurable, imagine it to falling deeply in love or becoming addicted to tranquilisers. Of course, it is not in love with you. It is in love with a real or imaginary spirit entity which they tell their followers is the god of all religion. They call it Shiva Baba or "BapDada". They encourage individuals to believe the Brahma Kumaris and their deceased guru are their true Father and family, and that their biological families are at best obstacles and at worst impure, ignorant and devilish. Literally. That goes for you too if you do not submit to them.
Very quickly, celibacy comes into the picture. This is a total celibacy. No nothing. Not even love and affection. If she is becoming hooked, we can take you step by step through what they will likely say and do to her, how they will work as a group. They encourage a total surrender and dedication to their spirit being. They call it a marriage. Probably, at this point, she has not even been told about BapDada and they are just using general words like "The One ... The Light ... The Father" and so on.
It might not as bad as you think ... if she gets hooked in, it is worse. Don't be conned by the fact that the introductory course are free.