Why does Mal insist on communal suicide?
Why does Mal insist on communal suicide in Inception? If they were really still dreaming, she could just die alone and kick Cobb on the level above (if death would wake them up, it means there are no synchronized kicks needed). Murder-suicide would be another option. From her point of view, this would amount to helping a deluded person and her solo suicide as negligence.
Of course, she ends up committing solo suicide, but before that, she first spent weeks/month (?) trying to persuade Cobb and then executed an elaborate scheme that involved having three psychiatrists declare her sane and wrecking a hotel room. The alternatives would have been much easier. Her instinctual resistance to killing her husband would probably have been weakened, because she already did it multiple times during their boundless dream-exploration.
In my view, her focus on communal suicide points more to mental illness as opposed to actually believing they need to wake up.
You can't wake somebody up from Limbo with a kick.
The movie makes it clear that, for a kick to work, you need to be able to sense it in the next level down. In Limbo, you have no sense of what is happening in the levels above at all - you are completely removed. You can't simply kick somebody out of Limbo because they can't sense it at all - you have to follow them in.
I have no explanation for why she didn't think to kill Cobb and then kill herself, though.