If getting herself away from the power struggle and the game of revenge meant that she and her baby would be safe, she was gladder to take this selfish step.
It wasn't like Alessandro Marino's death would affect her in any way. He was the biggest threat to her unborn child and if Santiago could kill him as he expressed his kind words in a very unkind manner, she would be more than thrilled.
She couldn't kill him with her hands as she knew it wasn't possible. If she killed him, she would never be able to leave the nightmare behind. Even after his death, he would haunt her. So, it was better to kill him with a borrowed knife.
Or it was better to lend the knife called evidence that she was looking for to someone capable of fucking over her daddy dearest!
It didn't matter to her who that person was as long as he/she could complete the task.
As for this man, she couldn't read him like other people. He was as deeper as any abyss to read him out.