Hello Sheila,
Disney has three levels of hotels: value, moderate and deluxe. Since you mention you would like a 'nice and affordable' hotel I will tell you about
Disney's All-Star Music Resort (which is a value resort). Most value resort rooms only sleep five people, but the All-Star Music resort has a limited number of 'family suites', which sleep up to 6 Guests. They have a separate bedroom with a queen-sized bed, a pull-out sofa and 2 single sleepers in the living room, 2 bathrooms and a kitchenette (which has a fridge, a bonus if you need that for special foods or storage of items for your granddaughter). The All-Star Music resort is our number one choice. We love the pools and a wonderful atmosphere.
In regards to possible needs of your granddaughter: first let me say that I have not traveled with a person with diabetes. As Disney is excellent at serving guests will all types of needs, I am certain that you will be able to take the items she needs into the park - call 407-WDISNEY now to find out if there is a special procedure to enter the park, what help there is at the park, and where the help is. If you have any trouble, stop in at guest services as you enter the park. As you book any restaurants or character meals, be sure to mention it to them, and then again when you enter the restaurant. Be sure to also mention it when you book your room reservation so they can provide necessities, like a 'sharps' container (which I understand is no extra charge).
Sheila, you are all in for a truly magical family time together!