From her road bike size, I'm going to say the smallest made. I'm 5' even, with a short reach. I would not fit on any Surly - last time I looked, every model in the smallest size is too long in the top tube for me, way longer than a short stem would ever fix.
She also would likely never fit on an adult size cross bike - a 46 cross bike is probably more like a 50 road bike - they measure out "smaller" because the bottom bracket is higher, making the seat tube shorter, but the rest of the geometry is more like a much larger bike. I ride a 44cm road bike with 700's, or a 47cm road bike with 650's. I can barely stand over a 44cm Redline and the reach is way longer than I can tolerate. I have a conquest 24 to mess around on. It is a little small. It's the only bike I've ever had that I've had to put a long stem on (I think I've got a 100mm on there) and it is heavy, but it works to have a little fun on.




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