I caught my daughter (4yr old) touching her private parts under the blanket. I also caught her using the shower hose and spraying it there. I asked her why and she replied it felt good. What is the best way to teach her about this?

My daughter previously will not wear pant at home and showed her private part to her brother. So I borrow some books that are suitable for young kids to teach them about their private part and how she should protect them (e.g. not to touch the private parts or let people touch/see). After she understands the reason behind, she stopped doing it. Some times, my girl will tend use her hands to scratch her private part. I will check if the private part is red/swollen. If there is nothing, I will bring her to wash with clean water and she will not do it after that.