Personally, I think you'll be fine, but I am a Disney lover, so I am sure you'll get lots of responses trying to dissuade you from bringing a 2 year old into the parks.
A few suggestions, though.....I'd cut out the Animal Kingdom.....I just don't think she will get much out of it at this age (certainly not much more than you can get in your local zoo for much cheaper). It gets really hot there and the park is laid out in such a way that you do a lot of walking, that tired/hot/damn, I want to get back to the hotel-kind of walking.
If you need to see animals, take a couple of hours and go over to the Animal Kingdom Lodge. It's a neat hotel, never busy, great design and theming, and the best part is that you can go through the lobby to the courtyard where you can see many giraffes and other wild animals, nice and close. No crowd, no cost, and you can leave when she decides she's had enough. Nice gift shop there too, and some great restaurants.
Could probably pass on SeaWorld unless you are dying to go there.
She will love Downtown Disney and you will too. No admission fee, first of all. If she is into Legos, they have a great Lego store and play area there that will keep her busy for a long time. Several other great stores that she will have fun at (Once Upon A Toy, World of Disney). Go early in the day to avoid crowds.
The Magic Kingdom is a given. I'd plan on 2 days there if she is enamored with the characters and you think she will sit for the parade and such. If you are going at an off time (NOT Easter) you will be able to see and do more than if you are going over a school vacation time.
I'd suggest a character breakfast to really see her eyes light up. Depending on her favorites, the Crystal Palace in the Magic Kingdom does one with Pooh/Tigger/Eeyore/Piglet that is fun. Or the Princess breakfast in the Castle (Cinderellas).
If you don't want to use valuable park time at a sit-down breakfast, there are good character breakfasts at the Contemporary, Grand Floridian, Polynesian as well as other hotels where you don't need a park admission to get in.
You didn't say when you are visiting but if it is in the summer, cut your schedule down....way down....due to the heat. You don't want to push a 2 year old in the heat. And you don't want to spend your vacation listening to all the other 2 year olds who are tired and overheated either!
Staying at a Disney hotel offers convenience and constant 'theming'. Makes it easier to go back to the hotel for a breather. A hotel on the monorail is ideal but you'll pay dearly for the privilege. Even the less expensive Disney hotels make the trip more fun.
Don't forget the water parks. She might really love Typhoon Lagoon or Blizzard Beach. And nothing beats a cold water ride in the Orlando heat.
Remember, you'll be walking all over with a 2 year old and a grandma. You aren't going to be buzzing through the parks like you might have when it was just you and your wife (sorry!). Plan ahead to maximize your time. But most important, have FUN!