How do I know if she likes me?

If she goes early, or stays 'til the end, you do the same. If necessary, tell her you need a breath of fresh air and see if she follows you outside. Once on your own with her, hold her hand, and smile, and see what happens.

Worst case senario is you'll have to actually open your mouth to utter the words "I really like you, do you want to make something of it?"

From the sound of it she's as interested in you as you are in her, but simply play it by ear, be gentle and and drop as many subtle hints in the form of body language and physical contact as possible.

ahh do you know how annoying it is reading this? you're a big boy now, make your own choices.....

fantastic, I reckon you'll get the St George Cross for bravery

Do you know how annoying people like you are?