The executor paid the final bills/debts with the money from dad's estate, are the heirs billed to pay it back?

If she paid bills for your father as an executor, and the money came from HIS estate, your FATHERS money, then you owe her NOTHING. She did not pay with her own money. She paid those bills with your fathers money, as she's required to do because she was appointed executor. Your sister has pretty big ones if you ask me. Was there an attorney to probate? If so, I'd make a call to the attorney. Good luck, she sounds like fun.