She maintains eye contact. Ever see a girl stare at a chocolatey dessert or a cute dress in a store window? Girls use their eyes to convey desire. If she can't keep her eyes off you, you're in the clear, especially if her pupils appear wider than normal.
She starts to act like your reflection. When people are attracted to each other, they start to mirror each other's actions and speech patterns. If she starts saying weird phrases that only you use, it's not because she's your other half (though hopefully that's true, too); she just likes you.
She keeps asking questions. Questions are a good sign that she's really interested in who you are. If she keeps asking you questions and actually listens to what you have to say, it means that she's invested in getting to know the real you.
