For one thing [Cassie] was a woman, which caused a certain amount of poorly sublimated outrage. (1.22)
Rob mentions that the Murder Squad—heck, most of Ireland, in fact—is still stuck in the 1950s in some way. This removes the Sepia tint nostalgia of the novel's opening scene, and replaces it with a reminder of 1950s Mad Men-era misogyny and discrimination.
Cassie was only the fourth woman Murder had taken on. (1.22)
The police force in Ireland (and probably everywhere, all over the world) is a total boys' club, so Cassie faces an uphill battle for respect from her superiors and her peers from the very beginning.
The grapevine claimed, inevitably, that [Cassie] was sleeping with someone important, or alternatively that she was someone's illegitimate daughter. (1.23)
This is mentioned around the time that we're told "Cassie was only twenty-eight." So are these remarks ageist, sexist, or a little bit of both –ists?
We went through the predictable process where Quigley and a few of the others spent a while asking me whether I was shagging her and whether, if so, she was any good; once it dawned on them that I genuinely wasn't, they moved on to her probably dykehood. (1.72)
Not only are the male officers misogynistic, assuming that Rob and Cassie must be sleeping together (of course, we can't defend them once they do sleep together), they also turn homophobic in a way they wouldn't with a male officer. No one suspects Rob is gay because he doesn't sleep with Cassie; they suspect she is.
"No real man could actually be beaten by a little girl." (2.4)
Cassie is often very sarcastic about the prejudice she's subjected to from the males on the force, or in this case, from the male worms in the computer game Worms.
[O'Kelly] dislikes Cassie for a series of mind-numbingly predictable reasons—her sex, her clothes, her age, her semiheroic record—and the predictability bothers her far more than the dislike. (2.17)
We imagine her gender is at the top of O'Kelly's dislike list, and that he wouldn't dislike her for the other reasons if she were male. And it's funny how she hates him for hating her for such unoriginal reasons. Misogyny is so 1950s, dude.
"I walked straight into it. You're some woman, all the same." (6.57)
Even the witnesses, like Mark the archeologist, are misogynistic. Mark seems to think that Cassie tricked him during her interrogation because she's a woman, not because she's a cop trying to get information.
O'Kelly made a few derisive comments about headaches being "womany s***e." (11.82)
Yes, only women get headaches. Good thing you're in charge, O'Kelly.
"We'd always shared everything." (13.51)
The worst treatment of women comes from the teenage Jonathan Devlin and friends who view women as property to be passed around and used. They never once think that Sandra has thoughts and feelings of her own—she's just their instrument.
"Women can't afford to wait like men can, you know. And being a detective must make it hard to have a serious relationship, doesn't it? It must be a lot of pressure for her." (17.63)
Rosalind is being manipulative here. (When is she not?) But she speaks the truth in some way—it is a lot harder for Cassie to be a detective as a woman. Although the issues Rosalind speaks of aren't necessarily at the forefront of Cassie's mind now, they might be later if she wants to start a family of her own.