Idrill the Traitor

[Rune Son of Bjarne]

I stumbled upon a rather interesting bit of text about the fall of gondolin. (as it is told in The Book of Lost tales)

Originally Posted by The Book of Lost Tales - The Fall of Gondolin

And another rede she gave him, and this he took also, that certain of the bravest and most true among the lords and warriors of the Gondothlim be chosen with care and told of that secret way and its issue. These she counselled him to make into a stout guard and to give them his emblem to wear that they become his folk, and to do thus under pretext of the right and dignity of a great lord, kinsman to the king. "Moreover," said she, "I will get my father's favor to that." In secret too she whispered to folk that if the city came to its last stand or Turgon be slain that they rally about Tuor and her son(. . .) Yet to Turgon she spoke not openly, nor suffered Tuor to do so as he desired

I am of course not suggesting that Idrill is a traitor, earlier in the text it quite clearly states the motives for convincing Tuor to build an escape tunnel and form his private guard.

I am however questioning her way to go about it!

When a person forms his own private guard and his followers starts encouraging others to rally behind him in case of the kings death, it starts to look like the preparations for a "Coup d'état".
Through history many people have been executed for less. . .

So is it just me or was this a very clumsy way of preparing for the worst?
Did Idrill (and Tuor) not take a very big risk by acting as they did, could they not have isolated Maeglin politically, make him loose the kings favor or just work on having the loyalty of the other houses of Gondolin?