Well she is comfortable enough around you to put her head on your shoulders so I'd give her a call or text her if I were you. You don't have to think of this as such a big deal. Just say hi and ask how her summer is doing. When you do this, be casual about it and don't put too much hope in her because that tends to make people act all awkward. Just have the mindset that she's simply a friend who you want to spend some time with and start talking to her. Remember that when you're talking to her, be sure to ask questions about herself in order to get her talking if you're having trouble with that and then after some time, casually drop the question if she wants to hang out. I know, it's easier said than done, but you won't know how it goes until you try! Good luck!