Why didn't Faile tell Perrin that she dealed with Masema and that he is dead now?

Contrary to her relationship with Rolan - which Faile understandably also doesn't want Perrin to tell about - I don't really see why the "Masema-massacre" should upset Perrin that much. After all, Perrin realized as well that Masema is crazy, especially after he tried to kill Perrin through Aram. And Perrin did shady things as well, e.g. allying with the Seanchan.

Besides that, Masema was the whole point of Perrins trip since ACoS, and Faile should realize that it might be quite important for Perrin to know what happened to Masema, if he eventually reports Rand about everything that happened. If Masema is considered alive, he might still be a threat so that Rand and Co. might consider to send someone to deal with him, which wouldn't be necessary if Faile truthfully told that she already killed Masema & his followers.

So, I don't really see the point in Faile's lie about Masema, except for hiding her true ruthlessness from her husband.