5 year old daughter masturbating

I have a 5 year old daughter and she has gone through phases where she masturbates frequently since she was 2 years old.  I have talked her and do not feel there is any abuse that has happened.  I realize that this behavior is normal for a child her age and I have tried really hard not to chastise her or embarrass her when I have talked to her about the subject.  I have told her it is something that is private and to only do this when she is alone.  The problem is she does share a room with her 4 year old sister and she has started masturbating with her sister in the room.  I found her doing it under a blanket, and I believe she thinks that makes her alone.  Anyway, my question is how do I let her do what she needs to do when she doesn't have a place to go to be alone?  

[dragonlover91]

u should tell her to either do it in the bathroom while no1 is in there with her or to only do it in her room when her sister is not in the room but i wouldnt worry about it too much

[allmymarbles]

You are involved in a social, nor a moral, problem. Such behavior may be normal, but it is not acceptable, and could have unpleasant social implications. I would tell her she can't do it at all. No if's and's or but's.