Considering Foucault's ideas, who is 'mad' in The Glass Menagerie?

I would say that Amanda could be considered "mad"
according to a Foucauldian line of thought.  If one believes Foucault's ideas that
society uses the notion of madness to demonize others and create a realm of exclusion,
and thereby substantiating their own power, Amanda stands to benefit the most from
Laura's designation of being "mad."  The idea of Amanda standing to benefit from Laura's
being considered as "mad" is logical.  It allows Amanda to ruminate about her own youth,
and how she is running the household in an effective manner.  Laura's different
approaches to life and in being a woman threaten Amanda's state of being and stature in
the world.  While she might consider Laura to be "different" and a bit "mad," in the
end, it might be Amanda who is actually insane, using the designation to demonize her
daughter in order to make herself feel better about her life and the choices within
it.