Gee, I wonder

Oldest e-mailed her teacher and said she was worried about youngest.  Youngest doesn't answer her messages on facebook.  Oldest really got along well with this teacher and they have kept in touch since she moved on to the higher grades and since moved.

Let's see - you tried to mother youngest - and mother in the sense of  bio type of mother - not the nurturing type of mother.  You made your sister lie for you and keep secrets.  You have not called the house once since moving.  Your messages claim that you and bio miss her soooo very much.  No phone calls, no letters, no birthday card, no birthday present, nothing but a rare facebook message.  Oh wait, the birthday present you told her was being sent on her birthday now a month later you tell her hasn't been bought yet.  But as soon as the town opens up for tourist season bio will be sure to buy her a gift and mail it.  Oh wait, will that be right after she sends son his present.  I mean after all his birthday was in December.  And bio herself told him she was sending him the boots he wanted.  (The ones we bought last summer) 

Let's see bio has called once since you moved.  That five minute conversation caused youngest to have nightmares for a week.

When you moved youngest sighed a big sigh of relief and said, "I'm glad she's gone.  I don't have to lie and keep secrets any more."   A week ago a teacher asked her if she missed you.  She came home to tell us.  And asked what her answer was she said, " Not at all."

So oldest, your sister is just fine.  Actually her and your brother are doing great since you left.  They are calmer, the stress you put them under is gone.  School is going great.  She loves her new room.  She loves being honest.  She loves being able to dress the way she wants, say what she feels and wear her hair the way she likes it without you tattling to bio.  You may miss your sister because you are alone in hell but, hey that was your choice.  If you want to believe all the lies bio feeds you go right ahead.  But, your sister isn't buying it from her or from you.