Once a certain amount of time has elapsed, the revelation will be less of an issue. She can write it off claiming "Well I was all traumatized from my captivity, and hearing that he tried to kill you made me snap." This is one of those things that isn't going to be a big deal down the road, but in the heat of the moment could cause all sorts of unecessary arguments.

If it gets too problematic, they can always reveal the truth. Given all that is on Rand's plate, Maseema is very much an "out of sight, out of mind" issue. Rand isn't going to worry about him if he is not making any trouble.

And too, assuming she's actually thought through all the ramifications is kind of a leap. Much more likely, it was a reflexive, "Spot threat - kill threat" type of reaction, that she carried out because she was PO'ed at Maseema for trying to kill her husband, recalling the arguments about his disposal from before her capture and wanting to actually act with the upper hand and exert some power for a change, after so long in the underdog/clandestine role.