Most important question is -- what does your daughter need? And, what do you need to know in advance so you can make sure she is ok and your family has a good time?
We took our son to WDW for the first time when he was 8. (While not on the spectrum, my son has many characteristics of kids with ASD - sensory, ADHD, anxiety, tics, etc.) I spent a year planning for our trip - we stayed at Pop Century and he was fine. He had always been extremely afraid and anxious around costumed characters of any kind, so I didn't book our trip until I knew that that would not be an issue any longer. We gave him many opportunities to be around characters (Sesame Place, parades, sports events), and when my dh volunteered at his school to dress up as a character, my ds was the character "helper." That was what "cured" him of his phobia. After that, I knew we were a little closer to Disney dreams. This happened around age 6.
Next - anxiety about dark, scary rides. We watched a ton of YouTube videos and rode hundreds of rides virtually, over and over and over. (He also has OCD.) We read lots of books about WDW written for kids. Over and over. If a ride had a scare factor listed, we watched the video.
I used Touring Plans and made a very detailed plan for every day we went to the parks. I shared the plans with him and I verbally rehearsed our days, step by step, with him so he could visualize it. And then, I stuck to our plan, and kept telling him what was coming next. If there was anything he decided he didn't want to do, after a little talk about it, if he didn't want to do it - we didn't do it. Changing plans with a little adult disappointment for not going on ride is a lot easier than dealing with a meltdown in the middle of a hot park. We also had decided that returning to the hotel when needed was important, but we identified places in each park where we could go to cool down or have some downtime too. We spent close to 2 hours on Tom Sawyer Island on 2 separate days on our first trip.
Finally, we used a GAC and it was the best thing for us. The cast members were very supportive. On Pirates, his very first ride, he got very anxious before boarding the boat. I asked the CM if he could use his little flashlight (very important to have one of these at all times), and not only did they say yes, they even gave us our own boat!! We have had many magical moments since then!
My son loves Disney so much, he wants to be a CM when he grows up! He is now 12, and has been to WDW 8 times in 5 years, and on a
Disney Cruise. He is obsessed with how things work behind the scenes, and we have been lucky to have met many CMs who share the magic with us! Also, pin collecting is a favorite activity for him, and it has really helped him with his social skills. And - there are rules for pin trading, and he likes rules!
So, I really think that over-planning and previewing are what helped us with our first visit, and we have had wonderful visits ever since. We went into it with an open mind, and also with a commitment to making sure he was ok.
Know your kid's likes and dislikes, fears and triggers - and plan with those in mind.
Hope you have a great time planning, and a great trip!
Lorri