She didn't say it, at least not as the press has been telling it. What she said (video, w. included spam) was really interesting, actually; she asked herself if it might be karma, and then she was notified by the Tibet Foundation that the Foundation was supporting the earthquake victims. So she was summarizing a lesson in compassion. When the press got ahold of it, they retold it to make it sound like she was scolding China, and China, claiming to be above criticism, made a big foofooraw about the whole thing ("You'll never work in this country again.") Rather like what's been done to Hilary Clinton, actually, and I begin to wonder if it isn't what the press usually does to women who usurp the male prerogative of moral criticism. Stone has, not unreasonably, objected that she is being treated unfairly and the facts seem to bear her out.
But karma, in its most basic sense, means "action". Used in the ethical sense it means volitional action, choice, and by extension the direct and indirect consequences that follow on choices. So, I rather doubt that the physical quake had much to do with China's karma. Yet if China spent 1/10 of the money and effort on building safe structures in Sichuan that it spent in conquering Tibet, there would probably have been very few deaths during the recent earthquakes. Seismically unsound schools? How could they? But greed knows no limits, and no shame. So, the quake wasn't a result of karma, but many of the deaths were. May China learn from their karma.