Trust- Even our greatest gedolim had rebbeim. Is it possible for a woman to learn without a teacher? Of course. But it’s also more likely that they will misunderstand many things without a teacher. Same thing with boys. If you want to learn anything properly, you need a teacher.
Lior- like I said before, S”A also says that they receive reward for learning it. So you have to reconcile the two. Saying she is allowed to learn but no one is allowed to teach her is illogical and certainly not what the S”A meant.
And if I understand PAA correctly, he is saying that Chazal knew that in their time that it was bad, but since they understood that the reality can change, they refrained from making a formal prohibition. Hence, the S”A never says it is assur for them to learn or it is assur for anyone to teach them.