Remember that drop bars will stretch out her reach a lot further than the flat bars. If she`s comfortable with the reach as is, it`ll probably be too long with drop bars. Does she object to the current bars for some reason? Maybe her hands would feel better just by adding bar ends? Maybe trekking bars on that bike too? Any rate, if you go swapping bars and cockpit stuff on it, I suggest locking it into a low-ish gear with the derailler stop screws (temporary SS mode) and just hooking up the front brake so she can test ride it with the different possibilities before you get too far into any conversions. No sense getting it all set up just to find out it needs a shorter stem or totally different bars or hates the shifters, or whatever, right?