It's difficult for me to give someone good advice that I don't know on a personal level, so I just speak from my own experience. You're young, and most girls your age are just looking to enjoy themselves and experiment, which is what I would recommend you do as well. It is much more socially acceptable for females to make public their promiscuity these days, and so much more of it is out there now because of the internet, cell phones, and digital cameras. But if this is such a turnoff for you, just move on to someone else who's at least more discrete about their sexual conquests.
As for knocking out a girl at work, it will eventually create some drama when things turn sour, but if she says she gives great head, go for it. And be sure and tell her you've had better afterwards, and they'll keep on coming.
"Yeah, well, you know, that's just, like, your opinion, man."