Wolves at the Gate by Persephone Black

Assassin Scarlett Fletcher is supposedly dead. Lyssa intends to make it so. Just…not yet.
Lyssa, the Wolf of the Styx Syndicate, has a simple plan. Hide her enemy-turned-uneasy-ally, train her up, and use her to take down Grandmother. Then Lyssa will follow through on the kill order and end the assassin for once and for all.
But nothing to do with Scarlett has ever been simple.
As Lyssa and Scarlett work together to track down the elusive Grandmother, lines begin to blur. Every sparring session just brings them closer together, and it’s getting harder and harder for Lyssa to stay objective.
And when more secrets finally come to light, the Wolf must make an impossible choice.
Will Lyssa stay loyal to the family she swore allegiance to? Or will she protect the troubled woman who’s slowly been stealing her heart?