Is the stepmother guardian of my daughter?

My ex and i share custody of our daughter and visitation is every other week with each parent. We have been doing this for the last 6 years. The step mother is claiming to be "guardian" for my daughter-signing school papers as "guardian", calling the school and getting information, even though i notified the school too many times that there are two parents and no guardian. Stepmom even went so far as taking my daughter to a counselor without notifying me. As she would have the same last name as my daughter, I would guess that she even ped herself off as the mother. My husband (stepdad) knows that he has no legal right to sign papers or inquire at school, let alone take her to a counselor without myself in company. I guess the stepmom is above me and feels that she can undermine my rights as the Parent. The ex also feels that she can do how and what she feels is her rights to do. What is the law regarding guardian and parents? There are no court docs giving her guardianship.