You need a bedtime routine that is really calming. You need to tell them in the morning what will happen (bath- stories- song - sleep)
Tell everyone you meet what is going to happen and how amazing DD is for doing it
Ring people and tell them. Get her excited about how amazing it is to do.
Then
No telly for an hour before bed.
No big meal an hour and a half before bed.
Milky drink downstairs (never in bed)
Then bath (not every night unless you want to)
Wash
Teeth
Stories (about 20 minutes worth)
Quiet songs
Kiss cuddle
Then a very clear night night it's bedtime see you in the morning.
Leave room
When she cries first time say night night its bed time
Second Time say bedtime
Third time leave
If properly upset sing another song on repeat (twinjle twinkle x 20)
But lessen this each night
No picking up. No taking out of room.
Repeat the end bit in the middle of the night.
Obviously only do when she is well.
If you succumb and let her in your bed, pick her up or whatever that is entirely your prerogative but she will know for at least a week that that is a possibility and will keep holding out for it. Therefore you have some choices. Either just cosleep it works for a few people and might work for you but only do this if you want to really do it it's not fair to chop and change or keep doing what your doing or you do a clear ' your bed is where you sleep and this is bedtime'. My eldest is on the spectrum and never went to sleep before 10 but he knew from a young age he could never get out of bed so he just used to look at books for a couple of hours. I cannot handle not sleeping and as his main carer would be an absolute nightmare unless I got eight hours.
Think the main message is just to be consistent as children pick up very quickly on any loopholes!