Mr. Waterbrook's wife. Both the Waterbrooks use their dinner party as an occasion to remind their guests that the most important thing in life is "Blood" (i.e., good birth). Sure, "service, intellect, and so on" (25.76) are important, but it is Blood that really matters. Dickens is obviously poking fun at this sentiment.
Mrs. Waterbrook means that you can see the marks of family resemblance in a nose, which shows a person's lineage. But what she says is, "We see Blood in a nose, and we know it" (25.76). And yes, we have to agree with her: if we see a bloody nose, we do recognize what it is. Dickens is making a play on the word "Blood": for Mrs. Waterbrook, it means good breeding, but if you take it literally, yes, for all of us, blood is what really matters – after all, without it, we are not alive.