I think this inflexibility of mind may also give Lady Russell a bit of a blind spot. Mr. Elliot expresses opinions that Lady Russell likes and she thinks well of him for it, never questioning his sincerity.

Anne is more perceptive:

“Mr. Elliot was too generally agreeable. Various as were the tempers in her father's house, he pleased them all. He endured too well, stood too well with everybody. He had spoken to her with some degree of openness of Mrs. Clay; had appeared completely to see what Mrs. Clay was about, and to hold her in contempt; and yet Mrs. Clay found him as agreeable as anybody.”