is described in the following paragraph near the beginning, in relation to her feelings on the retrenchment:

CH. 2 -

"Lady Russell was most anxiously zealous on the subject, and gave it much serious consideration. ***She was a woman rather of sound than of quick abilities***, whose difficulties in coming to any decision in this instance were great, from the opposition of two leading principles. She was of strict integrity herself, with a delicate sense of honour; but she was as desirous of saving Sir Walter's feelings, as solicitous for the credit of the family, as aristocratic in her ideas of what was due to them, as any body of sense and honesty could well be. ***She was a benevolent, charitable, good woman, and capable of strong attachments, most correct in her conduct, strict in her notions of decorum, and with manners that were held a standard of good-breeding. She had a cultivated mind, and was, generally speaking, rational and consistent***;

...up to here we are well aware of how good Lady Russell is, and excellent she is, but like most people as has been discussed in the GR, she has weakness:

***but she had prejudices on the side of ancestry: she had a value for rank and consequence, which blinded her a little to the faults of those who possessed them***. Herself the widow of only a knight, ***she gave the dignity of a baronet all its due***; and Sir Walter, independent of his claims as an old acquaintance, an attentive neighbour, an obliging landlord, the husband of her very dear friend, the father of Anne and her sisters, was, as being Sir Walter, in her apprehension entitled to a great deal of compassion and consideration under his present difficulties."

So it's amazing, rank comes above her other values, when put to the test. Insomuch as she values Sir Walter because he has a higher rank, which fits in with her sense of honour, she wants Anne to be of the highest rank, and is blind to any other value in consideration of this.