Chapter 2, near the end "Lady Russell, indeed, had scarcely any influence with Elizabeth, and seemed to love her, rather because she would love her, than because Elizabeth deserved it. She [Lady R.] had never received from her [Eliz.] more than outward attention, nothing beyond the observances of complaisance; had never succeeded in any point which she wanted to carry, against previous inclination."

This passage supports the idea of Lady R.'s "blindness" to faults in those of rank or consequence. Lady R. seems to be oblivious to Elizabeth's slights toward herself, while being very alert to slights toward Anne. It seems she has a true affection for the family, and loves Eliz. despite the fact that she is undeserving of it. I think "it blinded her a little" is an ironic use of the modifier. She is a great deal blinded: look at the terrible advice she gave Anne on that basis. I think rank and consequence had a great deal more to do with her dislike of the Wentworth/Anne match than did his lack of fortune.