Do you need to hide in the anonymous section? Or was that an accident?
Does having had an affair bar a person from being a devout Catholic? According to your reasoning St. Mary Magdalen, Bl. Margaret of Cortona, St Mary of Egypt and a host of other men and women saints, were not devout Catholics. I'm not arguing that Maria Montessori was a devout Catholic, only that your premise is ridiculous.
I understand that her work was in children's education, not in "Catechism".
I have no personal experience of Montessori and her method, but I don't believe it precludes structure and discipline. Is there a reason that sound Catholic home school materials could not be used within the Montessori method. A long time ago now, but we mostly ever used texts produced by protestants, because that was what was available to us. But all three of our children, despite being raised in the conciliar church, have a passionate love for God and his Church, two of them being in Tradition and the other a devoted "orthodox" Catholic.
One should use whatever system is possible and suits your purposes.