I think you should take her
For our last trip to Disney, my son was 6 months old. It did take a bit of preplannng, but everything worked out just fine.
We got one of those bags that hang on the stroller, so we wouldn't have to worry about lugging a big diaper bag. We just made sure we had bottles with water and a formula container, a bunch of diapers/wipes, and a changing pad. It was so easy. We would time his bottle feedings for longer rides (TTA) or a show. He wasn't relying on baby food yet, so I didn't even mess with it on the trip.
I got him used to sitting in the regular seat in the stroller. I wouldn't recommend dealing with the infant carseats with the stroller. That would have made things more difficult on the bus. I also brought my Baby B'Jorn.
He was able to go on most everything with us...at least those attractions that my other children wanted to go on. The only thing I can think of was the Orbiter. I think he went on everything else that my 6 and 3 year old went on.
Now, we did have to do some advanced planning since I realized ds would not be sitting by himself yet. We were flying, and therefore, were limited with what we could bring. I knew we couldn't very well hold him or plop him in the crib every minute in the room. I got one of those no-frills bouncy seats (just your cheapest, basic one) that came apart. I was able to take it apart and pack all the pieces right in the suitcases. That was a lifesaver!!! Oh, and for baths we brought along an inflatable baby tub. The only problem was that we couldn't deflate it enough to fit back in the suitcase, so we ended up leaving it behind.
6-7 months is actually ap retty easy age to work with on a Disney trip. I've since added another ds to our family, so I know it will be more challenging next time, since he'll be 14 months. It sure will be fun juggling four!!