Requiem for a glass heart - David L. Lindsey

Irina Ismaylov kills men and women and she kills at the behest of Sergei Krupatin, the Russian crime lord who exerts a monstrous hold over her.
FBI special agent Cate Cuevas, still in mourning, has just learned of a devastating betrayal by her slain husband. Wounded and shaken, she is plunged into the most dangerous assignment of her career. The leaders of three international crime organisations are to meet in Houston. The implications are stunning, and horrendous. But the FBI has a chance to stop this unholy alliance, if Cate can infiltrate the Russian contingent - and if she can get out alive.
When Cate and Irina meet, they are drawn to each other, and as both fight to survive amidst the intricate and deadly stratagems of men of violence, their relationship becomes an intimate dance of sexual attraction and murderous intent.