Young child rubbing privates on things.

Hello, I'm not sure how to say this but my 4 year old daughter has been rubbing her private parts on things like couches, people's knees, chairs and ect. She has had the problem since she was 2 year old but not sure who to ask for help or what to do about it. Lately we just correct her by telling her," right now it looks like you are rubbing that area again. That is something that is not good for you. What you should be doing is not rubbing that area. If you need to you can ask us to rub your back instead. Because you did that you earned a chore." It helped her not do it as much but she is still doing it. But because its a touchy subject I don't want to embarras her in front of other people. So alot of time when people are around I tell her to sit the right way. I don't want to bring to much attention to it in front of them. If I can get her away I will correct her the first way. Should I be doing anything differently that may help? We are not sure what else to do. We truly appreciate any advice you may have.