No, but yes. Or is it? Yes, but no.
There are actual girl models. See the Trek models here. http://www.trekbikes.com/us/en/collections/womens/road/
However many bikes are unisex so if a bike that is being sold in the mens area fits you then you can ride it. I would say that a girl can ride whatever bike she likes if it properly fits.
Did you ask the employees at the store?