Won't tell me how much because she thinks I'll get mad, but it's at least $6,000 a year.

Out of how much she makes? Pre-tax obviously, and don't forget workplace benefits, bonuses and the like. See my point? She's sending a hefty chunk back home but the vast majority of the money she makes—and, more broadly, the GDP she creates—stays in America. To generalize your anecdote, according to the UN immigrants, on average, only send 15% of what they earn back home. To a wealthy country, this is frankly peanuts.