what's the movie with the boiled rabbit?

DD is obsessed with DS2. I don't know how else to put it. I know I've commented on it before, but it's getting so bad lately. Yesterday (which I'll tell about soon) she told me that she would rather go away with him than be in our family. That's interesting and really, actually, painful to hear.
The kids get home from school late this year...don't walk in the door until 4:35. Many times we have activities or even just dinner and they don't get homework done. So, when that is the case, they go to bed early in order to wake early (since DS1 has to be up at 6:40) and do their work in time for school. So, yesterday, DS2 had to get up early. I made the mistake of telling him his schedule in front of her. I think I learned that lesson. She went to bed at her normal time and YET...bright and early...as soon as I got Cole up...here she came. She was out of her room, hiding on the balcony to stare at him doing his work. After being caught (she's not quiet enough to sneak around in a silent house early in the morning) she lied and said that we were being too loud and she couldn't sleep. She received the pleasure of doing chores for over an hour while he completed his work and I sat and relaxed. If she's going to be up - she may as well be useful!
I kid you not, every time I looked at her, she had found a reason to be in the living room with him (the chores were in the bathrooms) - simply staring longingly. Ok, that sounds yucky - but there really isn't another way to say it.
According to her files, there is no sexual abuse...but I'm really starting to wonder. Can a 10 year old be this obsessed with a boy (who is her adopted brother...Jerry Springer comes to mind again) and, for the record, other boys without there being something else in her history? I just don't know.
We discussed how families work - used mine as an example. Siblings grow up together and care about each other - but mom and dad are the central people in a family. Then siblings grow up and leave their family. They remain friends and hopefully stay close in heart - but chances are that there will be miles between most siblings. Each person goes about life and creates a new family...it doesn't mean you lose your childhood family, but you are tied to your new one more firmly. I pointed out that when I tell a story and say "my family", I mean DH, DD, DS1 and DS2...none of whom were with me when I was young. Should I be talking about childhood folks, I start out by saying "My sister, L" or "my mother in XX". Did she get it? Well...her response was "I can move wherever he goes". So, no - I don't think so.
Overall, I worry about the effect of this on DS2. He feels sorrow for her so often. If he plays with her and moves on later, she tells him that she has no one except him. She guilts him incredibly. She is his shadow and he asks me for help - which I give him...but at the cost of him feeling even more guilty. I have to physically remove her many times from his side. It generally ends in him getting to choose where to play or what to do and me forcing her to be elsewhere (actually, she generally ends up with me in time-in). I am having trouble distinguishing a response to this one.