SPDmom, definitely talk to her pediatrician and ask for help. It sounds like maybe a sleep center could help too.

Have you tried melatonin to see if that would help? My kids mostly had/have trouble falling asleep, but are fine once they're asleep. I would also try moving her bedtime earlier by 30 minutes. I read Healthy Sleep Habits, Happy Child by Dr Weissbluth when my older son was a baby. He had a lot of good things to say. One thing that stuck with me was sleep begets sleep (the more they sleep, the more they'll sleep). I'm a very firm believer in early age-appropriate bedtimes. If they get overtired then their body will crank out adrenaline to compensate and then won't be able to get to sleep even though they're tired.

Does she still nap during the day at all? Kids this age need 11-13 hours of sleep. If she does, then a later bedtime is okay depending on how long and when her nap is. Both of mine stopped napping around their third birthday, so I moved their bedtime up to 7pm, sometimes even 6:45. Then they would sleep for 12 hours straight. I hated that limbo time when they would sometimes nap and sometimes not nap. Usually my older son would nap at preschool and then not be ready for bed until 9 or 9:30. But not nap when he was home with me so 7pm bedtime on those days. Family thought I was nuts or wanted me to stray from our schedule but my younger son was an awesome sleeper bjrth until about age 6. If we missed that window of time, then he got super cranky.