I don't know that it's terribly common, but my 4 year old went through something very similar last year. When he was 2 he was in daycare full time. I don't work summers, so he was home with me for the summer. He did not nap over the summer. When school started, he went to daycare in teh morning and PreK in the afternoon. He potty trained over the summer and was consistently dry when school started. Total regression. He didn't consistently use the toilet until November.
I would definitely try to address her overtiredness. See what changes you can make to her sleep schedule to help her get more sleep. Don't sweat the overnight accidents. Just buy some pullups and have her wear them at night. Don't make a big deal about it, just let her know that this is totally normal and will help her sleep. She doesn't want to wake up in the middle of the night soaking wet. This way she can sleep through the night and wake up happy and ready for another great day.
Give her time! It's a lot for her to get used to. And she will. But she might need some time.