Read Moiraine's comment about this in TGH. She obviously strongly disagrees with you about Lan's reaction if he were to be told a prophecy claims Isam is alive... which is why she chose to keep it secret from him.



You think Lan would not hate a Malkieri who serves the Shadow?



Well, I sort of explained my reasoning already. Faile and Tenobia have been described as rivals (think Berelain and Faile, to an extent). Faile rejoiced in advance at tweaking the nose of Tenobia with her marriage to Perrin (by the description of the sort of men she likes, she'll find Perrin impressive and envy Faile), and couldn't wait to tell her she's lead soldiers in the field... all to spark her jealousy. I suspect Faile's ambitions, her love of power, has a lot to do with her envy of Tenobia's.

Tenobia will respect Perrin's for a warrior and leader when she hears of him and what he's done. She won't like so much how much political power Faile and Perrin have gained outside her authority. Naming Perrin Marshall-General eventually would be a great way to get him under her thumb, and force Faile back into her proper place as Saldaean nobilty and subject.

Alternatively, she might also name Perrin in the hope to increase her power over her uncles (she ressents their authority over her, remember), by naming someone eligible (as Faile's husband) who owes his position to her, not to his power and influence with the other lords.

Of course that may also be completely out of her hands. The Council of Lords in Saldaea has a great deal of power. They may want Perrin as new Marshall General (if it come to that) whatever Tenobia wants.

Of course there's little question who Queen Zarine would want to be her Marshall-General if both her dad and her cousin died. This is another way, perhaps more likely, by which Perrin could get the wolfhead baton before the series is over...