Hi Lenee ~
As a Mom to a son with special needs, I love to see that you are planning ahead! The Walt Disney World Resort is committed to assisting Guests with all of types of special needs including those with autism. They have put together
A Resource for Guests with Cognitive Disabilities including Autism Spectrum Disorder (ASD) that is available online by clicking on the link I've provided. That will give you some great information to help you before and during your trip.
You can only get a
Disability Access Service return time for those attractions and experiences that offer
Disney FastPass+ service. Anna and Elsa are very popular and their line tends to be long. Currently, their location doesn't offer FastPass+. If you are not able to go earlier in the day, I would recommend speaking with a Cast Member when you reach their location to see if they have any suggestions. I would be as prepared as possible to wait just in case. If your daughter has any comfort items including electronics, bring them if possible. Headphones or ear plugs help keep the noise level down in the parks.
If your daughter becomes anxious, remember to relax, and remove her from the situation until she calms down. There are quiet places in the parks to give her a break. A suggested list is provided on the link above or ask the nearest Cast Member. Know her limits. If you see that she has had enough, pack it up and head back to your resort. You may not get to do everything on this trip but you can make the most of everything you do.
Wishing you minnie magical memories :-) Allison V.