Ya, your girlfriend flooded her body with hormones. That's going to show itself in one heck of a messed up cycle. It should eventually go back to normal but Plan B is to be used in emergency situations which should by nature be very infrequent. What's going on with her cycle is probably due to all of the ipills. But also, her cycle will be very unpredictable and you won't know when she will next ovulate. Get some condoms! Use them every time!
I think your girlfriend should see a gynecologist and tell exactly what she took and when. The doctor will tell her if the hormones have done a lot of damage. You two should not have used the ipill that way.
Are you referring to the plan B pill specifically? That has a pretty high dose of hormones and were not really designed for use every time you have sex. It's probably a good idea to locate another form of birth control. Also, if you have a prescription and accidentally didn't take it as prescribed, it's always a good idea to give your doctor a call and just let them know what happened. If a period hasn't returned, and one was expected- you should also take a pregnancy test as a precaution.