She does not say, "I'm good," because she correctly understands that to be a statement either about her virtue (I'm good, as opposed to evil) or about her ability (I'm talented, as opposed to incompetent.)
Likewise, a lady does not use "I'm good" as a substitute for "No, thank you" in response to an offer for more of something. When asked, "Would you like more tea?" a lady doesn't say, "No, I'm good," when she means, "No, thank you."
Principle: A lady knows the difference between well and good, and uses them correctly.