Okay, first, she's going to have to do really light training this week. That shouldn't be a problem, cos she should be doing short distances this week in any case.
Next, if she's congested on the day of the race, it will make her head feel like it's throbbing. She ought to load up with a decongestant containing a painkiller.
She will also end up breathing more through her mouth, which will make her mouth dry, so she should look out for every possible watering stop along the way ... but don't drink at all of them, or you'll end up needing the loo. Do lots of "rinse and spits". I know it's a bit gross, but needs must, and all that.
A cold could also make her sweat more than usual, so maybe towelling wristbands would help, so she can keep wiping.