Always A Witch, by Carolyn MacCullough (sequel to Once a Witch, Clarion Books 2011).
Teenaged witch Tamsin must travel back to the 19th-century to do some serious foiling with her newly realized magical powers- if her foiling is not successful, the bad magical family might destroy her own, much nicer, magical ancestors. A pause ensues while the reader (at least, me) works hard to suspend disbelief as Tamsin, after wandering around for a while, not exactly fitting in with the locals, finds employment at the home of her enemies. After this point, there's no need to suspend disbelief with regard to time travel, as the book turns into a zippy magical power struggle. Tamsin's beau Gabriel joins her back in the past (good thing, too, because he's very helpful), and the bad family does nasty things with the blood of innocent victims. They are so busy, in fact, doing bad things that the complete inadequacy of their household staff (Tamisin, though a weak reed, is not the only problem) bothers them not a whit.
Some time travelish interest is added by way of Gabriel's gift--he can Find things, and one of the things he starts having trouble Finding is all the family that should still be safe in the present. The past needs fixing, and this adds a dash of tension that's a nice contrast to blood-letting manipulations.
So in short, Always a Witch is very fast, fun (though not for the victims) magical excitement, though not one to read for thoughtful reflections on the differing cultural mores of past and present! The good guys (Tamsin and Gabriel) are likable and their romance is romantic, the bad guys are nasty, the writing is just fine, and the magical powers being wielded against each other are nicely imaginative.
Don't try reading this one without reading the first, and since the first is also zesty entertainment, there's no reason to skip it. I'm glad I remembered enjoying the first; this one made a nice change from my standard middle grade fare.