My dd7 as Sensory Integration Disorder as well. You can get a guest assistance card at the Guest Services counter which is located inside each of the parks. This card can offer her an alternative waiting area for rides and if she is using a stroller they can give her a wheelchair tag for it so that she can bring it onto the lines.
I have found that using the stroller was a big help as dd could pull the sunshade/hood over hea & cocoon herself from the overstimulation of the crowds, noises etc. We have a BabyJogger City Classic that has a huge sunshade so she literally can cover herself almost to her lap. We bring earmuffs for her to cover hear ears on things that are too loud etc. Another suggestion is to hit parks early in the day and later at night. Afternoons are much more crowded, hotter and more intense in general. Take lots of breaks.
She also should go into the trip knowing there are experiences that her dd just may not be able to handle and that she needs to be okay with that. Rides like its a small world which is tame and fun for most people is sensory overload for my dd. There is the movement of the boat, the repetative music, the moving dolls, lights etc. For her it is just too much. Yet Space Mountain is fine for her. It is very dark and quiet and she craves the type of movement the roller coaster gives her.
You should check out the DisAbilities board for other tips.