Demons are Forever by Julie Kenner.
This is the third in the Confessions of a Demon-hunting Soccer Mom series. I haven't read the first, Carpe Demon, but I enjoyed the second, California Demon. When we left Kate at the end of that book, she'd just rescued her oldest child from becoming demon fodder, and has had to reveal her secret identity.
Allie decides she wants to be just like her mom, but she doesn't bargain on how dangerous the job really is. An encounter with a demon convinces her that being a research assistant is enough for the time being, and along with neighbour Laura and Kate's superior Father Ben they figure out the demons' latest scheme.
The covers of these books are a little confusing, as they imply they are primarily humourous. But although they do have a certain twisted wit, they definitely aren't funny books.
I'm looking forward to the next in the series, Deja Demon, which is due next summer.