Given that Phu Thuy is clearly an organized crime figure, I am suspecting that Atsuko is actually a professional hitwoman who was planning to lay low or even to retire in Vietnam after a particularly big job. Killing Yuri's husband was just a pro bono bonus.
I could totally see it. She killed a guy and didn't seem particularly phased about it, if she has criminal world connections I could totally see her being someone that is used to doing hit jobs for that reason, or any other similar jobs.