As a Catholic who has been observing his Church for over 50 years, it is not difficult for me to understand why Margie Winters as fired by the Sisters of the Immaculate Heart of Mary.
Catholic Doctrine states that persons who are homosexual have a "disordered" personality. Therefore, a homosexual is not considered in full use of their faculties, and that healthy relationships, intimate or otherwise, between homosexuals is impossible.
The presence of Margie Winters at Waldren Academy is a contradiction of that doctrine. A happy, competent lesbian in an apparently healthy, mature relationship with another woman refutes that Catholic doctrine, thus placing other Catholic doctrines under increased scrutiny and possible criticism. And this simply can not be tolerated at a Catholic institution.
Just as white racists might consider a competent black person as an "uppity nigger", a conservative Catholic would rather see a competent and happy homosexual as an anomaly. They would rather fire the "uppity nigger" and the "anomaly" rather than accept them and perhaps question their prejudices and doctrines.