First off, I'm not a doctor, but I know a good deal about meds.

Risperidone really doesn't do anything to help with sleep. In fact, I believe it can cause insomnia. It's used in children to to treat irritability and general disruptive behaviors.

Melatonin is a great choice as a sleep aid. It's naturally made in the human body (albeit at lower doses). It's non-addictive as well. It has few side effects, but if the child takes too much, she could be sleepy the next day. It's cheap in the U.S. and available without prescription. Did you ever try a lower dose? Some people don't respond well at any dose though, and they are always sleepy the next day.

Major boundary issues, severe trauma, sleep issues, and behavioral problems? Is the child overly involved with the parents or totally disinterested?

Reactive Attachment Disorder is fairly uncommon, but it's frequency is greatly increased in situations with major childhood trauma. (Especially switching caregivers) Children with RAD often suffer from sleep problems. It's not a primary symptom of the disorder, but a common associated symptom. They always have boundary issues as well. This is often behind many of their behaviors. I would check with a trained psychiatrist to make sure your child doesn't have RAD. You can read about it here: http://en.wikipedia.org/wiki/Reactiv...hment_disorder

IMHO, RAD is an environmental problem which doesn't respond well to medication.