WOW! After reading the posts, I must agree with this insight, completely.
Kids need stability, that's it. And, sounds like your husband has always seen his daughter as someone else's responsibility.
New custody arrangement would be prudent! Doesn't mean that there's a "winner" or "loser" under such circumstances - for crissakes, it's the kid that should be the focus, not the adults!
And, I read one post that makes a very valid point: you married this man KNOWING that his daughter had issues, and now you have the cheek to suggest that the child is destroying your marriage to this man? I'd suggest looking a little further as per what the causes of this kid's behavior might be. Then, I'd find a family counselor and get involved.
good luck
It's unfortunate that some of the constructive criticism is causing you angst, as I'm sure the posts aren't made with any malice intended.
I instruct children, as well, and have two children of my own - one is borderline personality disorder (now, an adult), and the other is ADD (just turned 16). In my many years of experience, I would hardly consider a child pouting, whining, making "potty" talk, or attempting to take something from another child tantamount to "behaving like an animal." And, I believe that you could have noticed, seen, or sensed that there were behavioral issues, even if you weren't having the child live with you half of the time.
If I were in your shoes, I would insist that my husband and his ex rearrange the custody/visitation schedule so that THE CHILD'S FATHER can interact with her and set reasonable limits and boundaries. I would further insist that THE CHILD'S FATHER and THE CHILD'S MOTHER arrange intensive family counseling for all parties involved. If you actually despise this kid as much as you seem to infer, the child is definitely aware of it, even if she is only 8 years old. Just because your child doesn't behave the same way doesn't mean that this little girl is a monster.
She is in desperate need and it is the responsibility of her mother and father to see that she gets the help necessary to circumvent serious issues, such as: self-mutilation, eating disorders, antisocial behavior, educational failure, risky sexual activity, narcissism, drug abuse, alcohol abuse, etc. That you can't define what this child's issues are only further necessitates the prompt action of her father and mother initiating family counseling. To wait until someone comes up with the Diagnosis of the Day (ADD/ADHD/ETC) is just damning that kid to irreversible damage. TRUST ME - my son who is BPD was a child just like the "animal" that your step-daughter is, and his father refused to acknowledge that something was wrong and, now that he's an adult, he's socially crippled.
<<Personally, I don't find posts spectacularly insightful if they contain sarcasm ("what are you doing picking her up from school ANYWAY?", "like most parents," sarcastic comments about how unrealistic it is to expect a child to do homework, etc.).>>
Either this person has solved the problem, or has experienced a raw nerve. Responding posts weren't necessarily "sarcastic," but rather an attempt to open the mind to see the entire picture. Quite frankly, some victims of emotinal abuse are suicidal, misdiagnosed as bipolar, improperly medicated, and actually seen as the "crazy" person. Only intensive family therapy/counseling will expose the roots of the child's behavior.
You're in a really difficult situation, and the main gist that I believe many responses were trying to present is that this kid needs immediate help and that the help must be initiated by her biological parents. The father of this child has no business foisting responsibility for this child's welfare (other than what could be considered reasonable) upon you - his daughter is HIS responsibility.
Now, if the mother is causing problems, it may be necessary to change custody/visitation arrangements so that the child will be in a structured environment. Having survived a child with borderline personality disorder and another diagnosed ADD, it is not only "trying" on the biological parent, but an absolute nightmare for a stepparent. The father of this child should, strictly for the child's well-being, intervene, ASAP, even if the mother is reluctant to assist! You should not be held responsible for seeing that this child gets the help that she needs.
Now, if I were in your shoes, I would not budge on this issue - either get help for this kid, or I don't want her in my home. Sounds drastic? Yepper. Sounds mean? Perhaps. But, from my own experience, a child with these sorts of issues is not only a danger to herself, but to others, as well. Again, my suggestion is: get yourself to a counselor, alone, if need be.
Best of luck to you.