When riding a road bike worry about top tube length not seat tube.
This thread is great!
When sizing a road bike you should concern yourself with the length and size of every part. The top tube and seat tube lengths are equally important. As is the stem length and rise, seat height, bar width, lever position, crank length ...ect. But whatever, I digress
The idea of a woman who is 5'8" purchasing a large mountain bike is ludicrous.