The world will never know. She might be, but Disney is too Christian to let the world ever know. They probably pay her off to never talk about anything sex related in any way, shape, or form.
Again, it's not like you know her personally, so why's it a stupid question? You don't know for sure, you're just some random run of the mill person who doesn't know her. You know what? Even if you did know her, it's not like she's announced to the world, "I am not bisexual." So it's ridiculous for you to insult someone for wanting to know whether she is or not.