Power laws are highly specialized, and a combination of some fed law but primarily state regulation, so the rules on buying back are probably pretty different from state to state, though it's so widespread I believe there is an underlying federal requirement driving it.
A lot depends on her own energy usage. If she is a complete green freak that takes cold showers and relies on a wood stove, primarily uses off-peak power and puts in peak power to the grid, and can shop and install the entire thing herself except the final hookup well, maybe she could eventually get ahead on it, but it'll still take awhile. Since that isn't really the case for 95% of the people who put in solar arrays, it sounds like she's bought into a total wagonload of solar power sales bullshit.