What evidence is there that Lady Macbeth is not as strong as she would like to believe, in Act Two, scene two of Shakespeare's Macbeth?What does...

In Shakespeare's Macbeth, Macbeth
returns from killing the King and he is hysterical.  It's as if his mind cannot grasp
what his hands have done. He tells his wife that the guards were saying their prayers in
their sleep as he entered to kill Duncan, and that when they said "Amen,"
he could not, though he felt that he needed a
blessing.

Lady Macbeth encourages her husband not to dwell
on it, but he cannot separate himself from what he has done. Still, Macbeth obsesses on
trying to find the reason that he could not say "Amen" as
well.

Lady Macbeth finally
says:

These
deeds must not be thought

After these ways; so, it will
make us mad.
(II.ii.33-34)

She warns him
that this kind of worrying will drive him (or them) crazy. This
might be an indication subconsciously on Lady Macbeth's part that
she is not as strong as she thinks. However, I think she is
actually quite capable at that time, but her situation changes
later. I would imagine that Shakespeare uses this bit of foreshadowing not only to hint
at Lady Macbeth eventual mental collapse, but I find it interesting that he presents
Macbeth as the weak one and his wife as the instigator at the beginning of the play, and
then demonstrates how they have switched places by the end of the
play.