Plan B can certainly cause all of the symptoms your GF has been experienced. That said, because it has a failure rate of about 25% she should take a home pregnancy test about 14 days after unprotected sex if she doesnt get her period by then.
I figure that the timing on her period wasn't right for pregnancy, and the discharge occurring the week after was a good sign. I'm just waiting now on her period to actually start.
I have also heard that if taken withing 24 hours the failure rate is only 5%. The 89% is a reduction rate of failure at 72 hours meaning that only 2 in 100 women will become pregnant if taken withing 72 hours. This risk is markedly decreased by taking it within 24 hours. I'm more worried about her health than anything.
Girlfriend got her period today, regular flow but some serious cramping (side effect of hormones)