Remember, November by Cameron Darrow

From the ashes of Allied victory, a group of witches will forge for themselves something altogether new in a time when women aren’t even allowed to vote. Or love one another.

Christmas, 1918. The Great War is over, and according to all the newspapers, Britain won. But for Millie Brown and her sister witches, it doesn’t feel like it. Brought together to try to end the war more quickly with magic, their failure could mean the disbanding of their budding coven and the overturning of lives already shattered by war and hardship.
It could also mean the beguiling French witch Elise Cotillard being sent back to France before Millie can work up the courage to tell her how she truly feels.

But when Millie’s best friend goes missing, she’ll have to find a lot more than just her courage. For when she turns up with powers unheard of in the history of witchcraft but no memory of who she is, bringing her home becomes Millie’s last, best chance at keeping her chosen family together.

And alive.

With no memory of her past, the woman who knows herself only as November has no idea why it has come back to try to kill her. The sudden manifestation of a power she can’t understand and barely control makes it all the more urgent, for the sake of everyone around her as much as herself.