Trouble at nursery

My little girl is at nursery and for the last three months she has been having really troubling behavioural issues. Really bad tantrums, screaming, hitting/kicking staff and other kids and yesterday she scratched someone. It’s usually when they get in her space. She refuses to nap when tired and really struggles to control her emotions. We have really tried everything to get her to nap, which she eventually does most times but she puts up such a fight. She has been having night terrors with separation anxiety and I think that is why she does not like to sleep. With emotions we have tried deep breathing exercises but that just sets her off more. Nursery is going to refer us to a specialist for her behaviour in January. Has anyone else gone through something similar? Is it tied to adhd or another cause? It just breaks my heart for her as she is so sweet and just feels like we are letting her down.