Adoption Gone Bad - Please Help!!

My husband and I received a phone call from Florida Social Services stating that they had our niece (whom I had only briefly met once) in custody because her mother (my husbands sister) had a drug problem. They asked if we would be willing to adopt her - there was nothing wrong with her other than she hadn't been to school in a couple of years and needed a place to sleep and eat. My husband flew to Florida the next day and was told that Florida would not allow us to have temporary guardianship, temporary custody etc. - we had to adopt her lock, stock and barrel. To add insult to injury - we had to complete the adoption in 30 days or she would be lost forever. Anyone who knows about the Florida Social Service System knows about the kids "lost", abused and killed recently. After receiving heavy family pressure, we agreed to adopt her - despite having just gotten married and having premature twin babies (in addition to our other two from previous marriages). We had to jump through an absurd amount of hoops in thirty days - from getting an adoption lawyer, having papers signed, medical exams, verification of income, personal recommendations, not to mention emptying our savings account. During this time, we were allowed to bring our niece home with us. She was an angel.... Until the ink dried on the adoption papers. After the adoption was complete, the real story came out. Our niece had been committed to a mental institution, regularly cuts herself, dealt drugs, slept with anyone willing and regularly steals and lies. If we discipline her, she complains to her guy friends how we mistreat her. I know this is a normal teenage thing, but we're talking guys who could easily break into our house and harm our kids or us. I fully expect to wake up one night staring down the barrel of a gun because I didn't let our niece go out. We have tried grounding, reasoning, positive reinforcement, bribary, ignoring her etc. We tried to get her to a therapist. She went, remained silent and refuses medication. I can't afford to spend that amount of money on a child who stares out the window every session. We've had to take her to the emergency room twice because she was so out of control we had to get her tested for drugs (she was clean). She's failing school, we constantly get calls from school because she's in the office for wanting to "kick someone's ***". She's had detentions, referrals. We're going to lose our jobs because we have to take so much time off to go to school because someone "talked about her" or "looked at her wrong". She's already been through one school. We went back to the adoption lawyer who told us we couldn't give her up/back to Florida - they won't take her. We may have to pay child support until she's 18 if we remand her to our states custody in addition to having an investigation done on our family/home because we are giving her up. We can't afford child support with four other kids and our home was perfect until she came here. Funny enough, when we adopted our niece, the family who pressured us to adopt her "disappeared" and her biological father, who didn't want to pay child support for the past 14 years "reappeared". He likes to "hang out" with her, but wants nothing to do with her outside of that. Her mother still has drug (and maturity) issues. I'm desperate at this point. I'm considering seperating from my husband so I can save what's left of our family. I'm ready to give up on the dream home we just had built a year ago. I need to preserve my little ones future at all costs. Please help!!