Whether she's being honest about not having feelings for you is irrelevant. Honestly, you need to learn to hold more respect for yourself and what's good for you. Hint: she absolutely is not good for you.
Also, flirtation is not a sign of anything deeper or meaningful.
Her face doesn't convey a light-hearted situation. That's your context.
And frankly, clarifying an openly disrespectful act as ok, because it's "light-hearted", is ridiculous.