racingchic, you would be well-advised to not simply buy a road bike you *think* is the right size. This is a certain recipe for injury and pain, believe it. Seek out an LBS that has a proper fit department and get it done right.
The shop I work for is one of the leading fit shops in the country, and all of our sales staff goes through
Serotta Certification. Wanna know more?
Here's who I work for -- go to the left-side nav bar and click on Professional Fit Services for more. The pages are a little hinked up at present, but still readable. Granted, we are a shop that employs over 75 people and have customers that come from all over the country and other parts of the world for our services, but there are literally hundreds of shops around the country that will have a fit guru on staff, likely Serotta certified. You can find one in your area
HERE. I cannot stress enough how important bicycle fit is for road riding. We have numerous staff members working 40 hour weeks in the shop just getting riders set up so they're not riding in pain. Many of these people bought a bike at a shop where it seems the primary factor was the salesperson wanting to just sell a bike rather than selling the right bike.
We also offer custom services throiugh several makers, for those who have physical limitations. We put them on the computerized size cycle and take a plethora of measurements. Those are then sent to the framebuilder/designer and the frame is built to fit that person's body specifically. We take this stuff very seriously and with good reason. You really can injure yourself on an improperly fit bike.
We also have new customers come in looking for a bike they've been recommended or read about, that they simply must have, and then we get them to test ride six or eight other brands/models that fit them better, and they suddenly understand.
You're obviously looking for a small frame. My wife is very petite, and rides a 49cm frame. This is her current road rig, an Orbea Mitis Dama:

Orbea, along with Trek and Specialized, offer women-specific designs such as the bike above. I strongly encourage you to explore these options as they are really doing a great job with this only recently developed angle of frame design. Heck, she is so small her hands couldn't properly reach the levers. I just installed a new Specialized WSD product that moves the levers 20mm closer to the bars -- she's jazzed!
Another reason to consider WSD (women specific design) is that you can get a small bike that still runs 700c wheels. Many smaller bikes will come spec'd with 650c wheels, but you want to avoid that.
And don't think that you have to be considering a $5,000 rig to receive this level of fit service. Any shop that knows what they're doing will provide proper fit on a $300 bike just as they would for a high-end or custom. We do it every day, seven days a week, and you can read on our
What You Say page why we do it.
Sorry for the long-winded post, but it is something I am passionate about and I really can't stand to see someone on a bike who isn't smiling because some spotty doofus bike shop guy needed to move a bike and found a willing victim. I'd not want to see a fellow vbmxer wreck her knees or back on an ill-fitted rig. Good luck and good riding.