Similar position. Very quick to tears, catastrophising the smallest set back, being defeatist, creative writing stopped, drawing stopped, painting stopped.
We tried speaking with her to find out why, and whether something had happened, but she wouldn't talk about it - in fact, asking about it made her upset.
The school reported that she was a happy, popular child, so it didn't make sense.
We tried to introduce things to look forward to (trips, etc) - as well as giving very clear praise when it was due, as well as reinforcing sleep routines, and increasing exercise, However, her negativity could often outweigh our efforts to maintain a positive atmosphere.
Finally, through conversation with the mother of one of her friends, we discovered issues at school that the school had not communicated - normalised bullying, being side-lined by the class teacher, and her crying at least once a day!
We had to enter into a formal dialogue with the school to assure quality of teaching as well as adherence to their safeguarding policy - to address the crap class teacher and persistent bullying. This was painful but resulted in new hires and external professional training for resources that remained that had been sub-par.
Our 9 year old is now much happier, and the creativity is flowing again.
It's worth double checking with the parents of children that are good communicators on how things really are at school.