I'm sorry, but as the wife of an internist, and someone who spends a lot of times with surgeons, and their wives, her elitist attitude is inexcusable. If you truly love your sister and want what is best for her, I'd bring it up to her, but in the spirit of love. Tell her that you feel that her lamentations about her unfortunate situation are relative to those who face true financial hardships. Express your concern about her increasing materialism, and about the snobbish comments you have heard.
The surgeons that we hang out with are VERY humble. One of them will be doing a pro bono mastectomy for my husband's aunt next week. Another one did my husband's colonoscopy and a sebaceous cyst removal, and when my husband canceled his appointment to get his sutures removed the surgeon drove over to my husband's clinic and took them out in the procedure room. They have nice things, but they don't flaunt their money.
I might also suggest that some medical wives use their husband's fortune as a Band-Aid for emotional pain caused by not having enough quality time together. I'm in a Facebook support group for wives of doctors, and I have heard a few say that when they are feeling neglected, they grab the credit card and go shopping because, "What good is all this money if I can't cheer myself up with it?" Yep, not my cup of tea, but it is what it is for some.
ETA: My sister and I have always held each other accountable for how we present ourselves to the world, and what kind of people we are turning out to be. If you are close enough with your sister you should be able to have this type of conversation without her feeling attacked.