my daughter is also six. and i have talked with her about good touch bad touch (as her doctor recomened.) ive caught her on a few occasions, and i think its normal for the age as long as its not to excess. and that they can learn that it is a private thing. to be done only when they are by them selves .but i feel that it should never be tuaght to be a "bad" thing. if she does get upset when you question her maybe its your approach or she has been punished for it befor...........but definitly clarify with her the differnce between bad touch good touch and that no one should be touching her body.
It depends on the excessiveness of the behavior, it is well catalogued by experts that a lot of this behavior can definatly come from being inappropiately touched by others,it is one of the signs they look for . As she was crying she could be upset as she would be, I think in this case you would do well to ask an expert what they think ,say no more yourself as if it is abuse you will only make her feel guilty and it is never the childs fault.
It is normal for children to masterbate. Children start to explore their bodies when they are just babies. For example when you might be bathing or changing their diapers, they'll try to touch their genitals. Perfectly normal. But on the other hand, does your step daughter live with you full time? If not, who or what is she exposed to at the other place of residence. Is she getting into trouble at the other house for doing the same exact thing? Hence the reason for crying. She probably thought that she was in deep trouble and didn't know how to respond. All you can do is talk to her about her private areas and calmly ask her if she has ever been touched in her private areas. Try play therapy. Playing with dolls and such. Little kids tend to talk through dolls and play. If need be, call some agencies out of concern and ask questions. Maybe take her to a doctor if you have that authority to.Talk to her father that you are with about your concerns and see what he thinks about it. I hope that this has helped you with your concerns. Take care.