Weird Dreams

I have a question about a dream my sister told me about. In her dream we were having sex, which is a strange dream but there is some background to the dream that happened recently. My sister and I are not close now, but when we were young we did sexually play with each other. She claims she doesn't remember anything about it but has problems with sex that indicates something happened when she was younger. So the question I have; is the dream about a wanted sexual encounter she is subconsiously wanting or is it about something different.