I don't exactly know my PBH, but my saddle is usually set around 74, so I can infer that I'm a centimeter or two shy of 87. I' am five ten. I am very happy with this size for me, although recently having spent some time on my friend's 55cm Cheviot, I would go 59 with that bike. I would think it depends a little on her riding style, but I would say definitely moving more into the 59 camp with 87-88. Consider the smaller size if the bike will be portaged up and down stairs frequently or the smaller wheel size is appealing for slightly more nimble handling (not a fan of 700c tires much over 40mm)--both were factors in my decision. Those are the only real issues since standover is eliminated and the Boscos go back lots. I imagine the incredible wheelbase of the 59 is even more Caddy plush, and I imagine Riv is leaning heavily this way, and I would go with their recommendation without hesitation (whatever it might be), as they have so much experience and so many data points. Good luck. I suspect either way she is going to love the ride of this bicycle. It is a true pleasure.

With the 52, her saddle will likely be set a good inch higher than mine here.