The Fine Line Between Your Agency and My Agency

I've been wondering about agency lately. Especially when I think of becoming a parent. I know we're put on this earth to teach our children and others who look up to us. We give them advice from our personal experiences, provide them with encouragement and love, try to give them the confidence and instill in them the proper values to make good decisions... but when that is not enough, then what?
I can recall a few times in my life when I felt my "agency" was being taken away and my parents were making decisions for me. At the time, I thought I had the meanest most unfair parents who had no clue about how to properly raise an independent teenage girl. Now I look back with gratitude and relief for the times that they stepped in and "took over" my life for me.
I want to help people. I feel the incessant need to "fix" people's lives and have difficulty staying separated from depressing situations. Nothing is more glorious than the joy that comes from knowing you've made a difference in someone's life. This is a feeling I live for, yet I tend to get caught up in not the most uplifiting situations in the process and find myself carrying a weight of sadness and anger for this world and the cruel people in it. I try to live by being supportive and loving and encouraging, but for one particular young friend, I believe the situation has crossed a line. This is one of those times my parents would've grabbed the reigns. Unfortunately, some people aren't as blessed with parents who know and understand the gospel of Jesus Christ. What do i do? I don't feel like I can stand idly by and continue to encourage, just for the mere fact that I'm not sure she is strong enough to make the right decision currently. Don't get me wrong, she is perfectly capable young woman, but I know what it's like to have moments of weakness.
I know I can't save everyone from experiencing hardships in life, but I would give anything to help limit it. So many young women today struggle with identity. They have lost a sense of who they are because of what the media tells them they should be. Sometimes we get caught up in making poor decisions and then suddenly we are struggling with self worth and thinking we will never do better. We don't deserve better. THIS IS NOT TRUE!!! We are all daughters of our Father in Heaven. As we truly come to understand this and His intense desire to bless us, we can attain a joy never previously imagined. I want everyone I love to have this joy. I'm just beginning to have a glimpse of it, and I've never ever been happier.
So again I ask, where is this invisible line between helping a friend and taking away their agency and doing as Satan originally wanted to do to us? Is it wrong for me to want to temporarily steer the bus? If so, I'm guilty as charged.