Forget she's staring at you.
Forget she's smiling the whole time.
Forget she's constantly touching you.
Forget she's laughing at all your jokes.

Instead, invite her to go somewhere else (to the bar, to a different area, to take some fresh air outside, etc) and see how she reacts.

If she goes with you, she's interested. If she comes up with lame excuses like "I need to look for my friends", she's not.

This is the only nightlife tip you'll ever need.