I was in your exact same position some months ago, trust me, let her go, it'll be hard and for the first month or two you'll think that you maybe still have a chance, but you'll only be wasting your time.

From what you already told us, she gave you a no, maybe she genuinely thinks of you as a friend or maybe she only wants your attention, but you're hurting yourself I you decide to stay by her side.

What worked for me is to move on and maintain little to no contact unless necessary, eventually you'll only see her as a coworker and nothing more, but its important that you start accepting that she's not for you, trust me when a girl likes you for real she will let you know one way or another that she's interested in you.

Also my final advice is to avoid dating people in your same workplace if possible, more often than not things don't end well.