One I doubt you are of the size to give advise on what a shorter rider needs, but IMO if OP is looking at a Tarmac they kind of know or should know it's one of the more aggressive race bikes to begin with, thus if they truly can't fit on a shorter bike there are plenty of really great bikes, granted the Trek Madone Gen 8 is even shorter so I would steer clear of that. Point being it's like going to buy a Ferrari and then complain about how it hurts to get in and out of a low to the ground sports car. I truly think a 52cm at there height unless they have a long reach is a better pick.