Book I read back in 2012, Main character was on front cover in form fitting leather armor. Main character was female. Main character was an angelspawn, and whenever in the presence of angels would go into "heat" (exact terminology used in the book). as an angelspawn, the main character was very fast and good at fighting. the plot had demons come from the ground in one part of the book. Angels in this setting are not looked at as totally favorable, since they try to stay away from normal humans and their troubles and only come in for "big" problems. I remember the series was put on hold due to a dispute the author had with her publisher, but she promised to try to finish the series with a different publisher. Setting was almost post apocalyptic if I remember correctly, I could be wrong though.
No one thought the apocalypse would be like this. The world didn’t end. And the appearance of seraphs heralded three plagues and a devastating war between the forces of good and evil. Over a hundred years later, the earth has plunged into an ice age, and seraphs and demons fight a never-ending battle while religious strife rages among the surviving humans.
Thorn St. Croix is no ordinary neomage. All the others of her kind, mages who can twist leftover creation energy to their will, were gathered together into Enclaves long ago; and there they live in luxurious confinement, isolated from other humans and exploited for their magic. When her powers nearly drive her insane, she escapes—and now she lives as a fugitive, disguised as a human, channeling her gifts for war into stone-magery and the pacific tasks of jewelry making. But when Thaddeus Bartholomew, a dangerously attractive policeman, shows up on her doorstep and accuses her of kidnapping her ex-husband, she retrieves her weapons and risks revealing her identity to find him. And for Thorn, the punishment for revelation is death….