While Francis Underwood's motivation and moral limitations (or lack thereof) in House of Cards most of the time seem rather clear-cut, his wife Claire and her state of mind sometimes stay a bit more nebulous to me. For this reason I'm also unaware to which degree she actually knows about Francis' more straight-to-the-point ways of rising to power, that being his direct murdering of at least Peter Russo and Zoe Barnes.
While the story of Russo's suicide isn't very hard to believe, Zoe's accident/suicide should look much less believable for anyone aware of her involvement in Frank's case. When Claire sees the news of that on TV she doesn't make much of a motion. But while I don't have much recollection of the particular plot of season 1 at the moment, I don't think they ever actually talked about any of those deaths directly.
So is there any indication that Claire Underwood actually knows (or doesn't know) of her husband being a cold-blooded killer? Or maybe she just assumes it without his awareness? But it might also very well be that this has been deliberately left ambiguous as part of Claire's sometimes less clear state of mind.