See if they have Shooting at Midnight by Rucka. It's a mystery novel/thriller that's part of his series about a male bodyguard named Atticus Kodiak but it's partially told from the perspective of his badass on/off-again girlfriend Bridgett Logan. Bridgett's a former junkie who agrees to go back on the streets/into the drug life because of a promise made to a friend. When she disappears into that life, Atticus starts investigating and her twin sister, a pretty badass NUN, gets involved in the investigation too.

Bridgett is one of my favorite female characters of all time, but ALL of Rucka's ladies are strong, awesome peeps.

Also, you might like the Beauty Killer series by Chelsea Cain about a female serial killer and the cop she's pulled into her thrall. Heartsick is the first (I think) and it's really good. I got a little sick of the series by book 3 or 4 but Gretchen Lowell is pretty twisted and her relationship with the lead is sickly compelling.