It's a tough one... I always relied on those who opposed me to not let me win - but there's often a better solution from trying the arguments. I'm glad Sarah never went home but I'm also pleased she was put back in contact with her Dad. That's what she wanted even if I couldn't hand on heart say it was what was best for her.
I think when you make arguments like this - you have to project yourself forward about ten or fifteen years and think about the kid coming back and seeing if any adults took them seriously or listened to what they said. That might not happen in this particular instance, I doubt Sarah has the capacity to request her notes.... BUT, if she ever did, she'd see the fingerprints of Penguin all over it, arguing for what she wanted and mostly losing... even if it was the wrong thing.
Like you said - not black and white. Difficult arguments all round and not for everyone. :o/