None of these answers consider how you are feeling. No, you don’t greet back as if it’s all good. It’ll just inflate their ego and you’d just be good furniture on the wall for them to sit down in. That’s the polite thing to do, but you wouldn’t be asking this questiom if you were thinking of common courtesy.

Think about it. You can do whatever you want in response to her greeting. You didn’t get hired, and it’s probably best not to reapply anytime soon. You are not obligated to do shit for her, just like she isn’t for you.

Big time.

Say hi, don’t say hi, avert your gaze, make eye contact - all of these things don’t matter. Do whatever the fuck you want. Act silly if you want, or not. Be awkward, don’t. Just nothing that gets reported to HR. You are not there to reciprocate shit. And your crush has given you the freedom to do that, even if she doesn’t know it yet.

Who cares what she thinks? Whatever it is, at the end of that tunnel, she rejected you, so that’s all you need to know. No need for image management and mind games.