Why does she keep messing with me?

I asked a girl that I really adore to have a sleepover at my house, she said yes, Now she's hogging the couch, keeps poking my shoulder when I'm not looking, and occasionally tries to tickle me?
She even sat down on my lap without warning!
She just turned 16 today and I'm 14 turning 15 in a month.
She's a really sweet girl, very shy at school though, she doesn't have any friends, which I really don't understand why, she's elegantly beautiful, and has an even more beautiful personality.

Anyway, why is she doing this? She keeps staring at me, even as I type this from my iPhone

Maybe she likes you

She likes you or doesn't get out much.