Is she too shy?

Soo there's this girl, and we've been talking on Facebook for a little over a year. We don't talk at school, like at all... And I thought that the reason that she never talks to me is cause she doesn't actually like me... But I recently learned that she's actually quite shy... I've asked her out multiple times and every time she said yes! But then before the date she cancelled... The last time I asked her out she said she was really sorry that she couldn't and that we would do something in September, she promised, she was 110% sure we would... Well now it's September and I just got my license! So should I ask her out again? And in person or on Facebook again?