Does my ex-husband's new wife have any legal right over my kids?

My ex-husband has sole legal and physical custody of our three children. He says that I can't take my kids to the doctor or sign permission slips for their activities. His current wife puts her name as "mother" on all documents and signs his name on permission slips and other forms requiring authorization. My understanding is that step parents do not have legal rights to minors unless she adopts them (she has not) and my right were not terminated. Does she have the right to take my children to the doctor and authorize medical treatments if she does not have legal rights?