Little Widow

Careless, stubborn, and just a little bloodthirsty, Tasha is everything Yelena so desperately pretends she isn't.

After her sister's death, Yelena dedicates herself to righting the red room's wrongs, taking down redroom facilities and tracing the newly freed widows. So there was truly nothing unusual in her latest assignment; to find and collect a child assassin, even if there was a suspicious lack of information on the young widow. However, as usual, things go wrong at an alarming pace and soon Yelena finds herself tangled in a web, sewn together with cruelty by Drekov himself long before his demise.

or

Yelena captures a slightly psychopathic child assassin and things escalate rather quickly.