let me know your size and experience. some petite gals can handle a powerfull machine and other cannot. It is all up to the individual.
I think starting out with a 250cc (ie. the Kawasaki Ninja) would be great. But you might be bored of it, so the next progressive step up would be a 500cc, also by kawasaki.
I would not recommend getting a 600cc yet unless you are above 5 foot 5 inches.
this is my two cents.