This sounds like my dd2
she would.not.sleep. from 18months to age ....6? Somewhere at 5 it got better at 7 things really turned a corner now at 9 it is just once or twice a month she wakes me.
It wasn't behavioral.
it wasn't anything we were doing wrong. I had 2 other kids who had been sleeping through the night for years and There she was waking and waking and waking me up. There was an underlying need.
One thing that really really helped was audio books. She learned to enjoy them and she could listen to them all night long when she couldn't sleep (locked down kindle fire, she couldn't access anything else but audible and it has the blue screen on it so she wasn't looking at blue light in the night turning on her book). I still hear her audio book going some times in the middle of the night.
The other thing was helping heal her gut and lower inflammation, we are still working on
Maybe you are already tried everything, but have you looked into the potential connection of conventional dairy and respiratory issues?