I am sure the writer's language was more thoughtless than oppressive. The use of the term 'covert Christian' is in the context of a paragraph that is a litany of negative observations leading to the conclusion that the women are disingenuous and artificial. If the writer had used the word coy or subtle, which you are suggesting was her actual meaning, rather than covert I wouldn't really have a problem. So maybe I am getting caught up in semantics. But as Cher said "words are like weapons they wound sometimes" so you gotta choose your words with care.
I enjoyed reading this but I have to object to the use of the phrase "covert Christians". Does the writer object to their religious beliefs or the fact that these women don't identify themselves as a member of that religious group at all times? It infers that Christians are some sort of menace, lurking in the shadows. Perhaps if people like the writer didn't associate being a Christian with being a "basic bitch" these women would feel more able to freely express their religious beliefs, as is their right.
I am so glad I am not the only grown up still re-reading the Anne books. I completely agree with your analysis about Anne after she gets married. Nothing interesting happens to her ever again. It's funny that so many of these 'crone' characters were either widows or spinsters. It seems to suggest Montgomery thought marriage crushed a woman's spirit. But wasn't Emily of New Moon just a little over the top, with all the 'flash' and the almost marriages and tragic romance? The Blue Castle and A Tangled Web are better for adult readers. And Rilla of Ingleside and I are BFF's.