You can't necessarily decide what size you ride based on what size someone else your height rides. First, look at the geometry charts for the 2 sizes - there may not even be a difference in reach (sometimes there isn't - breezers are like that). If her torso is longer than yours, you won't be as comfortable on a bike with a longer reach. If your torso is longer, it might be a better fit for you. Generally speaking, too big isn't better than too small (IMO). You need the right size. What did the shop say about the fit?
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