Good sound advice from DPS.
My running partner and I both came down with a head cold during the last weeks of training for an upcoming marathon, ~16-20 miles. I remember our pace time being a lot slower but we continued to push thru and kicked the cold in a few days. Stay tuned in with your body. Leave your ego at the door and remember slow and steady wins the race. Best of luck to your girlfriend! Is this her first marathon?