Brett's relationships often entail sleeping around, and are generally not very serious. We can see this in her multiple marriages and in her confession to Jake that if they were together she would be unfaithful to him. She is also open about this aspect of herself, as she tells Jake and even Mike knows about it. We can see this in the way they address Brett's relationship with Cohn, criticizing him for not realizing that it isn't serious and he is not particularly special to Brett. Though we don't know if Brett for sure slept with Cohn or not, the general principle is there. With her being so open about her sleeping around and many relationships, it might've been easy for the men close to her to feel disgusted by her, or at the very least disapproving of her actions, but we don't really see that, which seems to refute my point of her being slut shamed. However, I'm not arguing that the characters are slut shaming Brett, but that Hemingway himself is slut shaming Brett.
I argue this because of where Brett stands in terms of the plot. The conflict between Mike and Cohn and the conflict between Jake and Cohn are arguably centered around Brett. Additionally, Jake's relationship with Paris and his own inner conflict are also arguably centered around Brett. These are all major conflict points within the novel, not small sideplots. They all also seem to revolve about not just Brett, but the fact that she sleeps around and has these open relationships. The way that it is phrased within the novel is that if Brett could just keep it in her pants, these conflicts would go away. Indeed, it seems that Brett at least feels this way to some extent when she talks to Jake and talks of how horrible she is. However, it isn't necessarily just Brett's fault that these conflicts arise, it's also the fault of the men involved. If the men involved truly understood where they stood with Brett and where each other stood with her, then the conflicts would have a much smaller degree of importance. However, both Hemingway and the characters involved only seem to see this with Cohn, and that may be for a whole different set of reasons. It is in this way that Hemingway slut shames Brett, and gives the men little responsibility for their own actions in their affairs with her.