My dad brought home an Apple IIe when I was two and put it in the corner of my room. It was one of the first steps of what I would become some day. I graduated high school with a honor society honor (under scholar, which is the highest point you can get), and inducted president in journalism honors. I'm also in the art honor society for my education in photography. I've gone into college since then and taken audio engineering, and am currently finishing a 3D animation marketing certificate.
But because of that, I am also the most anti-social person on this planet. I spend a lot of time indoors, except when photographing and while at school, and spend a lot of time just keeping to myself. I have very little communication skills, and very little in common with most people I know. People have accused me of some nasty things, especially since I tend to leave and enter rooms without any notice. They think I'm going to do something that might send me to jail - Which isn't the case, but people have that in the back of their mind for whatever reason, especially since I have problems with my life in general.
I think by letting your daughter keep the iPad to herself, that you're opening the door to her becoming out of touch with life, just as I am. You need to encourage her to play with other children, and to be curious about the things around her.
iPads are also not toys. They have small parts, and a battery that can easily tear and leak if a blunt object somehow falls through the headphone jack or punctures the back. She is not old enough to be responsible for a device that delicate. Nor does she understand the concept of the device, other than that she can play games on it. I actually was at a gathering the other day, and let a friend's daughter look at my iPad Mini. She is about five or six, and she would just click on all the cute looking icons, just to see what everything was. I had to help her read some of the menus because most weren't simplistic enough to figure out what was play, what were options, etc. It was awkward, especially since I had some pretty graphic 13+ games that I was afraid she would try opening and I wouldn't have enough time to grab the device from her before she saw something like 2D blood and the like.
From a educational point of view, the main issue is that she would learn how to use the device for HER needs, and not the device in general. It would be like her learning about earth science, but her only focusing on rocks because they're the most interesting. She needs to get the whole picture, that there is weather, rocks, plants, the ocean, etc, like the iPad is a tool for many things, aswell as playing games.
She needs to learn to read before even bothering to be honest.