Mary notices that, unlike the ladies room, the women's college is way worse than the men's college. This leads her to realize that there are serious questions to be asked about Women and Fiction.
At the library, Mary finds herself face-to-face (or eye-to-text) with the angry sexism of male writers and The Patriarchy. She imagines the fate of Shakespeare's sister in this environment, and it is super depressing. This is really low: she finds herself getting mad at all the men who've been oppressing her and her sistahs.
Taking a deep breath, Mary steps away from a battle-of-the-sexes approach to these problems and instead says that men and women need to welcome the other sex into their minds—uh, so to speak—in order to write well. And women just need to keep writing.