What evidence is there that Lady Macbeth is not as strong as she would like to believe in Shakespeare's Macbeth?

Lady Macbeth fulfills her role among the nobility and is
well respected like Macbeth. King Duncan calls her "our honored hostess." She is loving
to her husband but at the same time very ambitious, as shown by her immediate
determination for Macbeth to be king. This outcome will benefit her and her husband
equally. She immediately concludes that "the fastest way" for Macbeth to become king is
by murdering King Duncan.

The almost superhuman strength
Lady Macbeth rallies for the occasion and her artful and sly ability are shown through
her meticulous attention to detail regarding the murder. When Macbeth returns to their
chamber she goes back to the murder scene and cleverly smears the grooms with Duncan's
blood. However, her morals had prevailed just a while before as revealed through her
comment that she would have killed Duncan herself had he not "resembled [her] father as
he slept."

Perhaps Lady Macbeth felt that suppressing her
conscience for the deed was enough and that later the thought of the deed would just
dissipate. The outcome is not this way, though, because Macbeth and Lady Macbeth often
cannot go to sleep, and if they do, they experience terrifying dreams. But still, Lady
Macbeth is able to maintain her sanity and composure during the day, even more than her
husband. She urges him to be light hearted and merry. Once she practically rescues
Macbeth from the frailty of his own conscience. When Macbeth sees Banquo's ghost she
creates an excuse to explain his odd behavior. She attempts to chasten Macbeth by again
questioning his manhood. When the situation grows worse though, she takes charge once
more and promptly dismisses the lords from the
feast.

Later, though, the burden of Lady Macbeth's
conscience becomes too great for her and her mental and physical condition deteriorates.
A gentlewoman observes her sleepwalking and consults a doctor. The doctor and the lady
observe Lady Macbeth sleepwalking, madly trying to cleanse her hands of the blood of
Duncan and Macduff's family. Still in her sleep, Lady Macbeth asks, "what, will these
hands ne're be clean?" foreseeing that she will never have peace of mind. She also
retells events of the day Duncan was murdered. The doctor tells the gentlewoman that
what Lady Macbeth needs is spiritual and not physical help.

Lady
Macbeth's condition worsens, and she goes in and out of sleep with delirious visions.
Macbeth asks the doctor to cure her or give her a drug that will erase the troubles of
the heart. The doctor responds that he cures physical not moral problems. Later, as the
battle ensues outside of Dunsinane, by unspecified means Lady Macbeth commits
suicide.

At the beginning Lady Macbeth finds strength to entice
Macbeth to murder Duncan and to follow through with the murder herself. As time advances
though, her pretended strength diminishes as she fights the torments of her conscience.
Tending to her conscience engulfs and destabilizes her so that she can not support
Macbeth against Malcolm. Lady Macbeth's attempts to suppress her conscience fail. At the
end she chooses death because she can no longer bear the torments of her
guilt.

To quote Bradley, ‘Lady Macbeth is
perhaps the most awe- inspiring figure that Shakespeare ever drew. Sharing certain
traits with her husband, she is at once clearly distinguised from him by an
inflexibility of will, which appears to hold imagination, feeling and conscience
completely in check.