She clearly identified as a girl from a young age, so I imagine it's unlikely that she'll regret this "decision." In all reality, it seems she never decided but was born with that mentality.
Hooray for her parents being open minded and accepting people.
And while I'm here, I'd just like to point out that the level of ignorance, transphobia, disrespect and outright hatred in this thread is pretty appalling. Stop worrying about an 11 year old's genitals, those are none of your concern anyway. ^_^ <3