Why does Elizabeth believe that Miss de Bourgh will make ''a very proper wife'' for Mr. Darcy? What does her attitude reveal about her opinion of Darcy?

Elizabeth observes Miss De Bourgh stopping by in her carriage and notes, "I like her appearance. She looks sickly and cross.-- Yes, see will do for him very well. She will make him a very proper wife." This seems to indicate that these qualities might be what Mr. Darcy looks for in a woman.