Thanks Bev for the great advice!
Our 4 yr old dd has panic attacks at the silliest things. Yesterday we were in the
disney store and they had tiny, like beanie baby sized, stuffed gorillas and she totally freaked out. For her it is a combination of fear, visual sensory overload and noise. She is afraid of the unknown and afraid of what she knows. She talks about how brave she is going to be on our trip and I know once we get there that will be down the tubes.
We have told her that she will have to wait in line with everyone even if she doesn't want to go on the ride. That is just the way it is. She seems okay with that (for now). Our plan is that waiting in line is the most anticipation building part and that possibly by the time we get up to the loading (in fantasyland) she will have gotten used to the introductory images and be agreeable to riding. If not, one of us will take her off to the exit while everyone else loads in. We have prepared her with pictures and told her that sometimes it will be dark. Last night we bought her a light up necklace at the children's place (in the halloween stuff) that has an on/off button and she can turn on her little light on the rides if it's too dark. She likes this idea because she is in control of that. It's a tiny light and will not disturb anyone else's experience.
We've also explained to her that this is Disney magic and mickey wouldn't let anything in that would hurt you.
Oh yes, her biggest fear are the villains characters you might see walking around. So, we avoid places where they hang out. Also, if there is a villain near something you want to get on (capt. hook at pirates of the caribean entrance) you can explain to their nearby handler that your child won't go in until Hook moves and they will walk him away a bit if they possibly can. They did this for us last time although Hook gave me a hard time over it. He looted my bag

But, he did move and we then got on the ride.
Take it slow. There is so much to see and do without traumatizing them. We don't ever tell her that we're going on any certain ride. We take her in and let her pick. If we ride fine, if we don't fine. We have no expectations of completing a touring plan so that works out good too.
And, as Bev said, our child LOVED Epcot WS and I know she will this time too.
Good Luck! Oh yes, our daughter is also big into 'if other little kids like me are doing it, I will too" so that may be a factor.