I don't know how much help I can be, but not knowing what the 'flirtatious' behaviour is, I am a little concerned that when you talked to your partner, she got mad at YOU.

I think I would try to talk to my partner again, this time, starting with asking for advise as you aren't sure what you were told by the third party was true etc. At this point, you need more information to make a better determination of what actually happened and if you should be feeling awkward at all. Once you know that, it will hopfully be easier to know how to proceed (or not) with this co-worker.

Take care *hugs*