I think this is all in how you look at it. Thick holds a good point in saying that she could come to him for advice in things that are hards to talk to parents about. I remember when i was 16 i would always go to my older sisters friends to talk about shit i really didnt want to talk to my sister about and they could help me out and tell me the right things and what to do. I guess just know when to draw the line, you sound like you already do.
