I love giants, I have had two(now have a litespeed) and my mom has the ocr c3. I previously had the tcr advanced limited(great first bike!) and then I got the '04 t-mobile women's race frame.
The only thing I have to say, especially since you are shorter is to test them all out! I am almost 5'6 and was on a small and the top tube was to long for me(53.5 i think, where my new bike is 51). It fit my legs perfectly, but not my upper body.

Even though Giant says they make women specific bikes, the only size that they actually change the measurements for is the XS.

But they ride great,handle great, good product for your money.

I would definitaly suggest finding a giant dealer and stopping in