Does it say don’t teach, or does it say, women should not learn. The difference being that there is no mitzvah of talmud torah, but if they choose to on their own, their is nothing wrong on their part.
In todays bais yackov type high schools and seminaries girls may not sit down in front of a gemara, but they certainly learn gemara. Many meforshei tanach routinely refer to gemaras in their explanations of pesukim and when learning these meforshim in depth, these sources are learned. Many of the things we say in the haggada on leil pesach are torah she baal peh, is there a posek anywhere that says, send the women out at these parts? It implies there is nothing implicitely wrong with learning a gemara. I don’t know what the mechaber etc.. mean, but it is difficult to say it is absolutely forbidden for them to be exposed to and even taught on some level, torah she baal peh. (The next statement is superfluos, but the CR being what it is, I feel compelled to write it) Obviously I am not saying anything lihalacha, I don’t even know if what I wrote is true, they are merely observations that say “look into this further”.