A couple of things to consider that may already have been mentioned or implied. Your daughter’s accidents could be anxiety related. Or there could be some control issues going on. If she senses that this is an issue that makes you crazy, she may be having “accidents” as a way of acting out. That’s not to say that this isn’t ADD related. My adhd daughter, who is 10 now, went through an extremely challenging period of time when she was your daughter’s age. There were no potty issues, but she was very defiant, and, sometimes out of control. It was extremely worrisome. So I wonder if your daughter might be going through something similar, even though it may look different with your daughter.
The thing that worked best to turn things around in our house was following the Kazdin Method (the book can be purchased on amazon) and working with a therapist who specialized in the Kazdin Method. Basically the “method” is about ignoring the bad behavior (within reason), and giving praise and rewards for good behavior. It sounds basic enough but I’d encourage you to get the book for details. Sometimes the details can make all the difference. The other huge thing with my daughter has been to remain calm and steady, even when her behavior is really bad. And this is the recipe that we still use today. She is still a challenging child, but so much better now than she used to be.