Just to expand on the converting a road bike theme, I just did one for my 14 year old daughter. She was in need of a new bike and wanted to move more toward a road bike. So a friend gave me an old 10 speed that he had in his garage that happened to be her size. I converted it to a 5 speed, added slightly fatter tires, a more comfortable seat, and a set of riser bars. It's a lightweight steel frame and it rides great for a fraction of the cost for a new bike.
If you will be getting the work done at your local bike shop, go talk to them about bike sizes. If you get the frame in your size, most anything else can be adjusted. They may even have a used road bike. How well they sell depends on where you live. They are quite expensive around me, go 100 miles south and no one wants a "skinny tire" bike. If you can find one, used ladies bikes usually go for less than mens bikes.
Good luck