Sleep (or lack of!)

Hi everyone, I hope you're well. hopefully this message will make sense as I've been awake since 2am and no longer feel like a fully functioning human being. I'm posting here in the hopes that someone will have the miracle cure for sleep problems. I feel like we've tried everything for my daughter (6) who is diagnosed ASD along with other medical complexities and a hearing impairment. 
I'm waking up with her all through the night every night, putting her back in her own bed and settling her back down. I think the root cause of the issue is separation anxiety, but if we try and go through the process of teaching her to self settle she gets so anxious about it that I begin to feel like I'm somehow torturing her. 
Paediatrician is aware of the sleep issues but wants us to try everything else before prescribing Melatonin which is understandable but also very exhausting and frustrating when all you want is some relief from being so tired ALL OF THE TIME.

Things we've tried/are trying - lavender oil on pillow, milk before bed, relaxing sounds, certain colour light to help stimulate sleep, dehumidifier blowing out lavender oil mist into the room, listening to music, practice runs during the day, reward chart, weighted blanket, a piece of my clothing with my perfume on, the list goes on, I just don't know what else to try.

HELP!