How do I ask a girl from my childhood that I haven't had contact with in years for a date using Facebook

I'm a 24 years old guy that never had problems with girls and usually I am chased by women, but this girl is making me nervous and I'm not used to it so I'm feeling lost. This is a situation I wasn't expecting and I cannot figure out how to better approach the matter.

The girl I'm going to talk about is a childhood friend that I've know since I was 3 or 4 years old; when we got into school she was my desk partner and that was the case for the remaining of our first grade. It happens that her parents had to move due to their jobs and she transfered from our school. She was a neighbor too and we used to play a lot together so it was "traumatic" for me when she left. It's safe to say she was my first crush despite the fact we were only 7 at the time. We would see each other once a year during summer when she would come to visit her uncle that lives right next to my parents' place. That was the case until 7/8 years ago when somehow I always missed her when she came to town. Well, a few weeks ago I found her Facebook profile and I friended her. A few days ago she liked a post of mine about politics and I took the chance to send her a message and I got to have a nice conversation with her. We've found out we've been living in the same city and studying at the same University the last 5 years and somehow we never crossed paths. That happened 20 days ago and I've been thinking how to ask her out. She is absolutely gorgeous, she is single, and from a little bit of Facebook stalking I found out we have a lot of common interests. My problem isn't the lack of confidence to talk with her, it's the fear of her saying no and that closing the door on future opportunities. I really would love to get to know her better. What do you guys think I should do to get her to say yes and seduce her using Facebook as I don't have any other mean to ask her out?