I agree with yngdad. As soon as they start to notice their "pirvate " parts it need to be made clear that is what they are private. But don't frighten them or make too big a deal of it. Just say you know that is private and only mummy and daddy etc are the ones to see or wash etc. I was actually advised with my daughters (i have 2 aged 5and11) not to say the doctor can touch them because often in abuse an offender will tell a child "its ok i'm a doctor or i'm a nurse in order to touch them inappropriatley. So best to kept to mummy and daddy, granma etc and if necessary the doctor if mummy or daddy is with them.
The best age is 3 when they really start realizing they have those parts down there u start making it clear that NOBODY except mommy,daddy,doctor,or whoever (grandma) etc is close to the child that they are the only ones to ever see or wash down there. Ur daughter should be told and aware of this now because u never know when it could be too late.