It depends on the personality of the betta you choose, since some females can be aggressive, or get stressed out being in a tank with other fish. But since you're starting with a big tank, you will probably be fine as long as you add a lot of plants and hiding spots. a lot of bettas don't like large open spaces, but they do love large tanks with plants to hide and rest in.
For community tanks, most people recommend introducing the other fish, and letting them get comfy in the tank, before adding a betta. Introducing the betta first might lead to her thinking all 50 gallons are her territory, and might end up being extra stressful for all the fish