Use the noun snobbery when you talk about someone's habit of treating other people as inferior. If your friend doesn't want to associate with people who have less money than she does, it's proof of her snobbery.
Snobbery is an unattractive trait caused by a person's belief that he or she is inherently better than others. Most snobbery has to do with social class and the idea that someone who has more money or went to a fancier school is worthier than someone who doesn't have these advantages. The root of snobbery is snob, which in 1800's British slang meant "person of the lower classes," but changed over time to mean "one who despises those considered inferior."