She is much better than she was thank you, sorry to hear you're also going through this with your DD too.
Going back to school helped, as did being very relaxed about bedtime and not trying to stick to previous routines, which was really hard. We let her keep lights on, leave her bedroom door open, we would say goodnight and offer to check on her multiple times as long as she stayed in her room during the evening and slowly things started to improve. If she was awake when we went to bed she would be quite stressed and apologetic about it, we tried to remain very calm and reassuring and not make a big deal out of it. Previously I was probably full of "you should be asleep, you'll be so tired" etc
Gradually we reduced the checking all evening, we turned lights down, we still leave doors open and we do a final check before we go to bed when sometimes she's quite lucid and other times is fast asleep. We don't make a huge fuss in the morning but do acknowledge if she's had a peaceful night.
I think it was a mix of things to be honest, some separation anxiety as a result of spending SO much time together, going back to school helped this a bit, us being quite fixated with the amount of sleep we felt she needed, I realise now she takes longer to switch off and I need to give her more time to wind down and finally a lot of patience. I think this was a phase, it did eventually pass, but at the time I thought it would last forever! Like with babies and toddlers, sleep equals sleep so the worse her sleep was, the more anxious and stressed she would get, I realised I just needed her to rest and be calm and had to do whatever she needed to achieve that without panicking she was going to be up until 10pm with us every night!
I know how hard it is seeing your DD struggling with this, hang in there, this will pass 