Depending on the age of your girlfriend's Focus, it could also be the fuel pump. I believe there was a recall on the failing fuel pumps on the earlier Zetec Foci. Best way to notice this issues is if car tends to stumble heavily while accelerating out of a right hand sweeping turn with about a quarter tank of gas.

Also, check out the wiring harness going into the bottom of the coil back. There are quite a few aged Zetec Foci who have seen melted wires from contact with the EGR (harness is too loose) or stretched/broken wiring coming from the plug (harness is too tight).