There is nothing wrong with what Negar did - anyone would make a similar decision.
There is nothing wrong that Mona did - She had voiced her opinion earlier against allowing Negar to choose. She was overruled. It is a question of being out of the game...not just a silly dinner. So what she did was right.
So, this whole episode actually shows that it is the guys who are sissy and willing to sacrifice a deserving female competitor to make sure that continue to rot in the Jungle for another week....even though Marc and Akash redeemed themselves a bit by changing their decision.