I think this is a slight misremembering of the Mercy Thompson books. The first book is Moon Called and it was published in 2006 so it fits your date:
Mercedes Thompson, aka Mercy, is a talented Volkswagen mechanic living in the Tri-Cities area of Washington. She also happens to be a walker, a magical being with the power to shift into a coyote at will. Mercy's next-door neighbor is a werewolf. Her former boss is a gremlin. And she's fixing a bus for a vampire. This is the world of Mercy Thompson, one that looks a lot like ours but is populated by those things that go bump in the night. And Mercy's connection to those things is about to get her into some serious hot water...
Mercy's love interest is the alpha werewolf Adam not a vampire, but everything else fits. The vampires hate and fear Mercy because she is a walker and her power allows her to find the vampires' hiding places during the day when they are vulnerable.
Mercy's boss at the garage, Zee, is an ancient Fey (not a demon) who we find later in the series is immensely powerful though he hides it behind the facade of a harmless old man.
The cover showing Mercy holding a sword and standing in front of some flames could be Fire Touched, though it's a spear not a sword:
Mercy gets covered in broken glass in Iron Kissed when she is standing in front of a plate glass window and an attacking demon shatters it. She has to have the broken glass picked out of her skin (by Adam, which leads to a rather more intimate encounter :-) but I don't think the book specifically says the glass is in her bottom - it just says it's all over her skin:
I looked like something out of a bad horror flick. Naked, I was covered from fingertip to elbow and toe to knee with marsh muck: it always amazes me how much swamp there is in the Tri-Cities, which is pretty much a desert. The rest of me sparkled, as though I'd covered myself with some glitter lotion instead of having a window broken over my sweat-covered body. Here and there were larger chunks of glass that dripped off me every time I moved—my hair was littered with them.
And everywhere, I was covered with tiny cuts that oozed blood. I picked up my foot and removed a largish splinter that was responsible for the small pool of blood that was growing around me. All the cuts were really going to hurt tomorrow. Not for the first time, I wished I healed like the werewolves did.
The Mercy Thompson books are unlikely to ever win the Man-Booker prize but they are well written and entertaining and I strongly recommend them to anyone who just wants a fun and enjoyable read. I loved the first book and read the sequels the day they became available on Amazon, though I feel the series went on for a few books too long.