Don't shit where you eat. For me not worth the potential aggro getting involved with a co-worker, especially one that sounds like the girl you've just described. Go for girls you actually like, your dick is doing all the thinking right now.

If however you insist you really want to get with her then adopt an abundance mindset, meet other women, show her you have options that you're pre-selected etc. You say you don't care for this girl too much, then do just that, don't pay her too much attention you feel she doesn't warrant. Potentially she could be the one to chase you, at the moment sounds like you're her lap-dog sat there listening to how she got fucked at the weekend. Not fun.