Rest in peace beautiful Suni

Hey guys. This is our beautiful Hamburg who we got in November. She was 20 weeks old. She arrived with 6 other chickens of various breeds but she was the only Hamburg, so smaller than everyone. She loved sitting in the middle of the food bowl while snacking all day. Last night I noticed she was chilling behind a chair and I wasn’t sure if she unwell or just getting some time out. I called the vet and they asked that I call back this morning as there were a lot of emergencies. I wasn’t sure that this was an emergency or if she was just being a bit quiet. This morning she was dead. I don’t understand why.