DD2 has never been a good sleeper. Even as a newborn she wouldn't sleep anywhere but in your arms, sling or the pram, and never ever slept in her moses basket. I ended up going down the attachment route for survival so she co-slept and bf for a year, then we moved her to her cot in her room (but continued bf until nearly 2 years - she refused to take milk from any other source). She wouldn't self settle, we had to resort to feeding to sleep. She's never slept through the night.
We have tried several sleep methods (consistently and persistently). Nothing has worked. She's like the flu virus, as soon as you find a vaccine, the behaviour mutates and you're back to square one.
Her issue is a combination of separation anxiety and asserting her independence (wants to do everything herself, always has done). Her behaviour is extreme. For the last year she has banged her head against the cot and then the wall (when she climbed out of the cot) repeatedly most nights. I mean full on violently slamming herself against the wall with a complete disregard for the pain. She's had huge bumps and bruises because of it. We even set up a camera in her room to record it as evidence - because at nursery she is an absolute delight and doesn't behave this way (but then, she's never alone in that environment, so why would she?)
The bedtime routine is calm and consistent, she's happy being tucked into bed but the second we leave the room all hell breaks loose. We discovered that her anxiety was linked to the door being closed and leaving it open an inch resolved the problem for a couple of nights (until the 'mutation' of behaviour) and then she started coming out to the landing and having her tantrum there. We can't put a gate on her door because she will climb over it or use it to bang her head.
She is 26 months old and we are now in a situation where (on the advice of the health visitor) we are trying the slow retreat method. Dh stays in her room until she falls asleep. Again, this worked fine for a few days and seemed to make her happy, she even slept through but then another 'mutation' occurred. Now when she wakes in the night she gets upset because dh is not there and she is basically demanding that he stay in her room all night, which is not practical. We've tried the Rapid Return for the night wakenings - what a joke that is! She just jumps straight out of bed instantly and screams in a full blown tantrum. I mean, she has learned to weaponize her scream and has found the pitch that damages your ear drums. She is doing this outside of her sister's door. It's just horrendous. Dh ended up sleeping in her room because there was no alternative, we all have work and school in the morning. We need to be able to function.
Please don't jump in saying, "you built a rod for your own back" as it is not helpful and also doesn't take account of the whole situation. She has teethed terribly from 8 months old. She has a big sister who needs (and deserves) her sleep so we can't just let her tantrum all night. She doesn't tire herself out with tantrums and she hasn't learnt (doesn't care) that banging her head causes serious harm. We've tried controlled crying (worked brilliantly with her sister, I'm a big advocate for it) and even resorted to cry it out (because quite frankly, we were at our wits end).
Worth mentioning that she is developmentally meeting all expectations for her age (bar sleep and tantrum behaviour being abnormal) and doesn't show any other flags for autism.
All the articles I've read online talk like all you have to do is apply their one magic approach to sleep and it's all sorted in two weeks - those authors have never met my child.
I'm really hoping someone here will be able to give some solid advice or even reassurance. We are desperate now. Completely exhausted and miserable.