“Is insomnia in children treatable?”

Yes ,insomnia in children is absolutely treatable and that almost never involves medication. Behavioral interventions are remarkably effective. You should discuss this with your pediatrician and obtain referral to a pediatric sleep disorders center through them. To give you a more detailed answer requires knowing a good deal of personal information about your daughter and is best done by her physician

Unfortunately, there are no FDA medications to treat insomnia in children. I would encourage you to read Richard Ferber's book, "Solving my child's sleep problem". A great resource for you and always discuss with your local sleep doctor and/or PCP.