then your perfect for a 250f. if you can fit on a 450, then you can easily fit a 250, its around the same size only not as powerful. just about any brand is good, if you want to stick with suzuki (which i recommend, its what i stick with), the rmz250 would be your perfect bike, you could also go for yamahas yz250f, kawasaki kx250f, or honda crf250, but no matter what you have a solid bike that wont let up.
also, i dont think it matters that your a girl (except for the fact that its hot, ur bf is lucky), a bikes a bike, regardless of gender.