If you're short a women specific hybrid would probably suit you best. Road bikes are more for training, and new they cost a lot more than hybirds.
Shop around, check out ebay and craigslist as well as your local stores and see what you can find.
on the road, you can expect to be able to leisurely do 20 kilometres an hour. You can easily ramp that up to twenty five kph or above, but keep in mind that strong wind will definitely help or hinder your performance depending on the direction.