Get there one hour before opening. That's key. MK opens usually VERY early that week...sometimes around 7:30, 7:45. Get a FastPass for the one attraction you do NOT want to miss, stand in line for all the others. Have a plan.
(My list of MK's don't miss....
Mickey's Philharmagic
Haunted Mansion
Pirates of the Caribbean
Big Thunder Mountain Railroad
TTA
Carousel of Progress
Jungle Cruise
Maybe Splash Mountain, if she doesn't mind getting a little wet)
By 10 a.m., the park will be crowded, maybe closed to admission by 10:30 or 11. I usually leave about this time, but since she's never been, just take it slow, relax, focus on the ambience. Have a snack or two, or maybe leave the park for lunch, tour the resorts. The park will probably clear out later in the day, so even if it closes for a while, it'll probably re-open around suppertime. The parks stay open later that week, so you will most likely have a few hours in the evening to enjoy the park. It'll be carnival-ape crazy, if past years are any indication...but you can still have loads of fun if you're prepared for it.