Her actions are actually self-centered rather than selfish since what she has is already hers. But in any case, yes, you might be able to help her see that, and I think I would try a little reverse psychology or whatever. The next time she begins whining about something like having to drive a Cadillac rather than a Rolls-Royce, jump right in with a "whine" of your own...

"Oh yes, my dear, I totally understand! Why, the other day at the market I had to settle for (whatever) when I so desperately wanted (something else)..."

Never mention her or anything she has talked about, just give her some live illustrations of the silliness she often conveys and then wait for her light to come on.