Because of the nature of your situation, you really don't know the natural's mother's friends, boyfriends, others in the house. It may be time to have the talk about "good touches and bad touches". Blood is thicker than water and this little girl wants nothing more than the love and acceptance of her birth mother. Sometimes children believe the divorce or her parents break up was their fault. They will do just about anything to secure the love of their parents to counter their feelings. You have no way of knowing what her mom said, nor can you. You will have to respect and accept that. But, you do need to ensure this child is at a safe place when she is with her mother. Start the difficult dialog today in a loving, comforting atmosphere. Let her know you will be there to love, help, and guide her if anything happens that makes her uncomfortable. Don't underestimate the tug-of-war for loyalty and acceptance going on inside your step daughter's heart over this situation.