I would totally flirt back at her.
Give her a kiss.
And most of all, stop trying to guage weather or not she's interested in you. Go for her.
It's great that she is already aware that you like her, and is already comfortable with you.
If she doesn't respond to your kiss, at least she would know you are not just sitting there letting her tease you.

I wish it were so easy for me. I would kiss the girl I like in a second if I wasn't afraid she wouldn't get caught and get in trouble.

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I am your poet in the night.