When she throws, does the disc flutter, or does it fly cleanly? The flutter is caused by off-axis-torque, which is exacerbated by light discs. If she has that problem, then you obviously would like to get rid of it over the long run. Throwing light discs will demonstrate whether you're doing it right or wrong. However, it can become extremely frustrating to keep seeing that you're doing it wrong. So, it might be better to try heavier discs, while still working on improving technique to the point that lighter discs will fly correctly.