I have the same problem with Amelia at night, she will sleep through but I can't get her down initially unless I lay on the bed with her till I know she is in a deep sleep. I spoke to my health visitor about it because I was physically drained, I would be fighting her to go to bed from 8-9 till maybe 2-3am.
We've been refered to Sleep Clinic ran by a health visitor and they give you the support and advice and new approaches to deal with the issue.