I am new to the series, just having started to watch it seriously (from the beginning) two weeks ago. the scene of the murder of Gennadi and his wife disturbed me more than any of their previous murders.
I agree that the setup was ridiculous: Elizabeth knowing the right window, the back of the building unguarded, the window unlocked (opening to a fire escape, no less)?
All that aside, and with the proviso that I've only watched it once, I believe Elizabeth came in (knife drawn) intending to kill him. When she heard his wife, she backed off and was trying to get out. But when she was behind the door, I didn't think that he had detected her. I think she saw an irresistible opportunity, and motivated by her dedication to the cause, her training, personal anger, bloodlust, or whatever, leapt at it. Then of course she had to kill the wife, even more horribly.
Then to top it off, the shot of the kid's show playing on the TV, telling us the even more terrible truth even before panning to the child. Not actually showing the kid discovering his parents, but leading to the inescapable conclusion that it would happen. Masterful!
