Hi Judy,
How adorable that your granddaughter has taken to calling herself Minnie after her favourite Disney character - that is so sweet!
You will be able to find Minnie Mouse in Epcot at the
Epcot Character Spot along with Mickey Mouse, Donald Duck, Pluto & Goofy.
Over at Disney's Hollywood Studios, although Minnie Mouse doesn't have a scheduled meet and greet as such, we have sometimes been able to find her in the Magic of Disney Animation building during previous visits.
Be sure to pick up a Times Guide as you enter each of the parks for information on what characters can be found where and when during the day of your actual visit.
If you would like to attend a Character meal, may I suggest
Donald's Safari Breakfast at Disney's Animal Kingdom or Cape May Cafe at
Disney's Beach Club Resort as an alternative to Chef Mickey's. My family have always been able to see Minnie whilst dining at both of these character meals.
(Please bear in mind that characters are always subject to change)
Wishing you a magical trip!