Just found female peach face dead in breeding box?

This peach face has had 3 clutches in past 12 months, each time laying 4 eggs,with only one egg from each clutch hatching, our first Little one is doing well and is 14 weeks old, she had another clutch not long after but the baby had a defect, and we had to have the chick put to sleep. Yesterday she was fine and had laid one egg 3 days ago but today my son found her in the hutch and it looks as if she had died through the nigh ht . Why would this be?