How does Marianna defend Elinor faced with Mrs. Ferrars?

As you can see below Marianne gets rather vocal when she feels her sister has been slighted;

"Marianne could not bear this.--She was already greatly displeased with Mrs. Ferrars; and such ill-timed praise of another, at Elinor's expense, though she had not any notion of what was principally meant by it, provoked her immediately to say with warmth,

"This is admiration of a very particular kind!-- what is Miss Morton to us?--who knows, or who cares, for her?--it is Elinor of whom WE think and speak."

And so saying, she took the screens out of her sister-in-law's hands, to admire them herself as they ought to be admired."

Mrs. Ferrars is angered by her outburst, but Colonel Brandon..... he finds her actions endearing....

"Colonel Brandon's eyes, as they were fixed on Marianne, declared that he noticed only what was amiable in it, the affectionate heart which could not bear to see a sister slighted in the smallest point."