Dear Prudence,
My mom let me and my brother breast-feed until we were each about 5 years old. She let us touch and play with her breasts for years after that. She never told us what sex was, and later when I found out, I felt revulsion at the memories of how I touched, and wanted to touch, my own mother. Now I'm 18, a senior in high school, and I have a little sister who’s 9 years old. Mom breast-fed her until really late, and now my sister feels my mother's breasts the way my brother and I did. My sister is my mom's last child, and my mother persists in treating her as a baby. My mother refuses to consider she could be encouraging inappropriate impulses in my sister. When I tell my mother that I'm grossed out and that my sister's too old for this, she won't listen. But I don't want my sister to have the same revulsion at her own memories and confused feelings that I suffered. I'm so disgusted it's keeping me up at night. What should I do?