16" is indeed tiny, but it's perfect for her regarding how often she rides, her riding style, and our limited NYC apartment bike storage space (most of which is selfishly taken up by my bikes, of course).

I might take off the freewheel and see if it's possible to swap out some of the individual cogs, or maybe popping a 7 speed 11T on there and not using the lowest gear might work.

Then again, it looks like the easiest option may just be getting a larger chainring. So I'll add an additional question: What's your favorite protected chainring? (She'd like to keep the grease stains to a minimum, of course, hence the attractiveness of the current protected chainring).