Crush at Work

Right, so there is this girl at work I've known for a while now and have a big crush on. She's a couple years older and has been giving me mixed signals back. We get on really well, flirt and she knows I'm into her. She's denied she likes me, but then keeps flirting with me and stuff/talks about me with other co-workers about how I put effort in etc and there's this guy she's talking to who treats her bad, but she's still kinda into him. Advice please