How is Mary Morstan presented as a character in chapter 11?

Watson, looking at Mary Morstan through the eyes of love, finds her quite beautiful in this chapter but also thinks she seems sad:

She was seated by the open window, dressed in some sort of white diaphanous material, with a little touch of scarlet at the neck and waist. The soft light of a shaded lamp fell upon her as she leaned back in the basket chair, playing over her sweet, grave face, and tinting with a dull, metallic sparkle the rich coils of her luxuriant hair. One white arm and hand drooped over the side of the chair, and her whole pose and figure spoke of an absorbing melancholy.

Watson has come to bring her the heavy box of treasure from India that Sherlock Holmes has recovered for her. He tells her it will make her one of the richest women in England. However, rather than respond with joy, as he thought she might, she answers him "coolly" and seems less than enthusiastic about the treasure. The only time she becomes animated is when he tells the story of how he and Holmes found it. She grows pale when she hears he, Watson, was in danger.
All through the chapter, Miss Morstan is presented as more interested in Watson than the treasure. For instance, Watson observes that:

At the sound of my foot-fall she sprang to her feet, however, and a bright flush of surprise and of pleasure colored her pale cheeks.

The lovely Miss Morstan is presented as not materialistic. She is not all that concerned when the treasure box is empty because she cares more about Watson's love than the money. This makes her a pure, virtuous, and good Victorian heroine.