I was assigned a social worker after i came out of the hospital ... after my little depression/suicidal incident in April.
My mom and my guidance councellor (who i had been going to a few times a month anyway) made appts for me w/ the school's social worker once a week. I went most of the time, but after a while it got harder and harder for me to talk, once she got close to the "real" problems. I quit going ...
But now i regret it. She was really nice, and before she actually started talking about things that mattered, i liked going to our appts.
Her rules were that she wouldn't tell anyone anything, unless I said to her "Maureen, i want to die" or something along those lines. Then it is illegal for her to hold that information, knowing what kind of state you're in.
Even if she is a family friend ... this is her profession. Don't look at her as your parents' friend, look at her as your social worker. Your diary. Tell her what bothers you, and tell her that you were scared to talk to her b/c she's close to your parents. I'm sure you'll be comfortable w/ her in time ... Just give her a chance!