I have autistic DC too. And we were at the HP studios in July this year. Luckily, the 2 i took (DS25 and DD16) were both in good moods that day and loved it!
If your DD is cognitively able, take her and let her sit in the cafe and faff about on her phone. There's a cafe ground floor straight ahead that has some quiet corners. That one did not get too busy when we were there and we went school hols.
If she needs constant supervision, you are going to need to plant some seeds! Confrontation and forcing does not work with autism.
I think you'll need to just drop in casually some good things, drip, drip , drip each day now.
For eg - "i heard they do butter beer ice cream and some great cakes in HP. I'm definitely going for that!" (Do not ask her if she wants any - make it a throw away comment, but check she has no ear buds in when you make it!)
- "i don't think we'll do that photo thing on the train - i heard you can sit in the carriage and pose for pics - don't fancy that"
"Oh, i didn't realise you can go right inside Dudley's house!"
"I hope it won't be full of little kids and screaming babies!"
Try to find out about it - the things you guess she won't like (posing for pics, maybe some of the push button animatronic things - try to drop in that YOU don't like the sound of it.
Things you think she might like - get them in. Just a comment or two each day now.
This sort of technique works with mine. Even if it only leads to " well, i will hate it but you're gonna make me come anyway so i will"
That isn't rude - that is coz they have changed their mind, quite fancy it but don't find backing down easy!
You can also try something like "There looks to be loads to do at HP. I think we might just eat out at Pizza Hut (pick her fave!) after.
Again, just as a throw away.
Good luck!
There is LOTS to see and it really is for all ages.