In Act II Scene 2 of Macbeth, what evidence is there that Lady Macbeth is not as strong as she would like to believe?

This is actually a very important scene for discussing and
analysing the character of Lady Macbeth in this incomprable tragedy. Having abandoned herself to
the forces of evil in Act I, and committing herself to murder and deceit, we rather get the
impression that Lady Macbeth has bitten off more than she can chew when it actually comes to
carrying out the act. Although it is she that has to goad her husband into seizing the
opportunity and making his destiny a reality, when it comes to the actual murder, she finds that
she is unable to commit regicide herself and is only able to lay the daggers ready for her
husband to kill Duncan and then to besmear the innocent grooms with Duncan's blood, thus
implicating them with the murder of their liege. Note what she says to
us:

Had he not
resembled

My father as he slept, I had
done't.

This quote therefore indicates
that conscience and moral scruples are not so easily disposed of as Lady Macbeth would like, and
that she is not, as your question indicates, as strong and tough as she would like to
believe.