Good question (btw it was her hubby Robert she killed). I think the answer must be that your question has a few of assumptions.
1) Was Robert actually "infected"? (IMO I'd say yes that seems probable)
2) Did she actually "kill" Robert or just put a bullet through his head? (Its possible Robert could have been recreated/revived if something wanted that, however it appears (to me anyway) that the idea wasn't to kill Rousseau but to drive her nuts.)
I'm guessing the "rules" of "infection" will be explained a lot in episodes to come.