If mishnayos and gemorah aren’t allowed, who said there’s a heter for them to learn meforshim, Ramban, etc.? What’s the differentiation? Sarah Schenirer didn’t teach those. She taught Chumash, practical halacha, etc. The Chofetz Chaim didn’t say to teach all the other things that are Torah she’bal peh that aren’t relevant to girls daily living. Just because some mechaneches running Bais Yaakovs today decided to teach those now doesn’t make it muttar. Which posek (names, please) permits teaching those meforshim?
One that Rav Moshe (YD 3:86) names as permissible, since it teaches them middos, is Pirkei Avos.