I am a WAHM, my daughter and I are together 24/7, and I am pretty sure that no one abused her. She spent very little time in a preschool, which is run by catholic nuns. It sounds unlikely that any abuse could take place there.
It's likely that she played doctor with some other child though. Last year she mentioned playing with another little girl and touching each other, and she said the name of the child was Anna. However, when I questioned the nun about little Anna, I found out that there wasn't any little girl named this way .
I think that her interest in the genital area might be caused by the fact I have hip-carried her in a sling for a long time. Carrying on the hip stimulates the genital area esp. of baby girls. As soon as I discontinued the sling, she started exploring the genital area.
I obviously try not to make her feel ashamed, and she does not look ashamed at all! Indeed, I have trouble getting her to understand that she should not engage in such play when there are people over or when she is visiting s/o else.
When cuddling, she also takes my hand and wants to be touched there, and laughs when I refuse to, asks me "why not?" . It's easy to guess that such behaviors are quite challenging from a 4 year old, however, I try to keep cool and always explain gently that this kind of play should not involve other people.
I obviously hope it's going to stop, but I'm not sure it will. The only thing I can do is give her more cuddle time and more roughhousing, since any form of physical play seem to reduce her extra need for self-comforting play.