Stillness
She is very young and it is far too early imo to start putting labels on her. What does she say at bedtime? Why is she crying then? What happens if she spends the night sleeping with her mum for example, as a temporary thing, rather than her just crying all night? Are they really leaving her to cry all that time so that no one else can sleep? If she’s ok eventually at school but finds it hard to leave a parent to go into school, has something occurred that has left her feeling a bit insecure? Can her parents give her lots of love and reassurance over the coming weeks, even if it means slowing down or making some changes for now? If she draws or paints with them, what does she do,…this is often revealing if a child can’t express themselves easily. Something has changed in her ‘little’ world and it may take her a while to process it. Often just love and attention will gradually be what’s needed, rather than a ‘label’.
I agree - far too big a leap to suggest ADHD, autism, etc. She has said she’s sad - there will be a reason, very possibly something an adult would overlook.