I would start looking into what parks you want to go to and make a little "pre-schedule". Since you aren't a Disney guest, I would find out what days are the least crowded for each park. Don't ever go on an Extra Magic Hour day. There are a couple books which might be worth purchasing, Birnbaums, The Unofficial Guide, and one I've just heard about "Passport", which I'm going to pick up next time I go to Barnes and Noble.
So I guess in a nutshell, I would check out some books, and then make "park day schedule". From there you know where you'll be for convenient meals.
I'm sure your grand daughter would love the character meals.
Above all, remember that she's only 5. We took my son when he was 6 and all he remembers is a duck at the campground we stayed at that was crippled and standing in the long lines. Knowing what I do now, I'd have avoided all that all together if I only had a 5 year old. I'd take my time, enjoy the characters and just "take in" the atmosphere. Get her an autograph book for characters to sign.
Spend time at Mickey's Toontown, playing on Tom Sawyer Island, have a big chocolate chip cookie at the Main Street Bakery, go to the boneyard at Animal Kingdom, the passport and Kidcot stations at Epcot, many of the rides might be just way to scary for her, so make your days easy and fun. If her heart is set on one or two of the rides at each park that are really popular, use Fastpass or get there upon opening and do those right away upon opening to avoid the lines and then spend the rest of the time just having fun.
Like I've said before, she "might" love doing a big packed schedule of things to do and rides, or maybe she'd just love a wonderful relaxing day spent with Grandma and Grandpa and those hugs from Mickey, Minnie, Cinderella and friends.