I think a smaller rider will find the generally tall top tube of a cross bike to be a hindrance. Cross bikes are made to have a taller top tube than a road bike for clearance when shouldering the bike over obstacles. When cross bikes shrink, this dimension often does not shrink enough. Often times a cross frame will be a half-pound or more heavier than a similarly sized road frame because of selection of materials and wall-thickness which determines the strength of a frames. Cross bikes have to deal with stresses a road bike only comes across once in a while.

A compact-frame road bike is the way to go for a pure-road bike for a small rider. At your size, considering a custom frame, although a bit pricey, might make the world of difference. You can also use CompetitiveCyclist.com's sizing calculator, which you will end up doing if you have a custom bike built. This is the best thing we've seen for getting into the ball-park on fit before you go into a shop.

In fact, all of our MTB and Cross frames were fully custom and the girls used this method.

That's just my $.02, and the new road bike based performance hybrids are also a great option.

XO- VK