I'm 4'11", and I'm wanting to lower my Vulcan500. The only places I have trouble are starting from a stop pointed up a hill. I can almost flat-foot the bike, and most of the time do fine. I just really have decided, after trying to adapt to riding a Ninja from which I could only get my toes down to the ground, and dropping it over and over, that it was very important to me to be able to slam my feet firmly on the ground. I did drop my Vulcan once, but being able to get at least one foot firmly down has kept me from dropping it repeatedly, and has kept the bike upright enough, that I didn't need help regaining it's verticality after testing the force of gravity. The world is not a flat parking lot.
If your heart is set on owning a sport bike, sit on lots and lots of them and talk to a lot of people about the cost and practicality of modifying them to fit.
I looked up lowering a Rebel 250. It looks like the most common way is to change the rear shocks to shorter ones. You could lower 2-3inches. If I poke around the internet more, I might be able to find a way to make it easier to reach the handlebars too.
I think when I was looking at keeping a Ninja250 I was riding, I could have lowered it about 2 inches. Lowering the rear of the Ninja without lowering the front sounded like, in what I read, would make the handling less like a sport bike, and more like a cruiser. The front would require around $300 in parts plus labor, my and my husband's, or someone else's. I don't know about lowering the front of a Rebel. I'm still looking, but you could look up some of the Rebel websites. That's what I did some of when I was looking for a bike to buy. I looked up any information I could find online.
I know that a lot of women love sporties, but a lot of us love our cruisers. Don't rule them out. Once you're out riding, the important thing is the accomplishment of keeping two wheels between you and the ground.