You should check if the gear ratios of the 3 speed are to her liking.

I've only ridden a few IGH 3 speeds, but am always surprised at how high (or is it low?) the gearing is of the 'easy' gear on the 3 speed. Much harder to pedal than the easier gears of a derailleur equipped bike, at least on the ones I tried. Imagine that being the easiest gear on a long ride with whatever hills you have.

Could be a deal breaker right there for the 3 speed.