You're just simply gonna have to start hitting on her more and see how she reacts.
"That's cute" (when she does something, doesn't matter what)
"if you keep being cute, I'm gonna have to start hitting on you."
You can also Do sexualized role plays: "I'm gonna take u on a date. We'll go to the Sizzler. You can anything you want. Even the six dollar steak. Then we'll go to the beach and let off balloons and we'll jump in the ocean...wait a second, now I'm just picturing u in a bikini...............ok, I'm back..and then we'll walk around the little beach town holding hands. And then I'll leave you there. I mean, you can take a cab back, right?" (credit Sinn I think)
Bottom line though: start hitting on her more and showing more explicit interest instead of just innocent flirting. That's the only way to tell. If she gets a little bit uncomfortable (which she probably shouldn't if she already likes you) then you can always release the escalation:
"Too bad you're such a dork
""Uggh, get away from me
"I put those smiley faces there just to express the fact that even the releases should be said playfully.
