I was wondering this too. If the world just 'gets too much' it sometimes seems like the only option is to shut down and get away from everything. I have some form of mild undiagnosed AS / SPID and I know what it feels like to have the world screaming at you (at least, that's how it can feel for me). When I get particularly bad, I can't string a sentence together; all sounds physically hurt; I feel like the world is pressing in on me; crowds make me feel like I'm suffocating; and the best communication I can manage is a random hand flapping. If this is what it's like for your daughter, it would 'make sense' of her running away, and also getting stressed and angry.
If she has these issues, she probably doesn't yet have the control of language to fully explain what's going on in her head (heck, even I can't fully explain it, and I'm in my mid-twenties!). You may need to help her with this somehow - perhaps through art, physical movements or using similes. If she can find a way to better communicate her needs and feelings, it may give you an opportunity to help reduce her stress and handle it when it happens. I know I'm making it sound like it's simple, but I know, it really isn't. Unfortunately there are no magic fixes for these issues, and there's never really a cure, but even if it just makes life a tiny bit easier, I'm sure it will make a huge difference to you.
As for what you can do at Disney, I'll give you a few suggestions, and you can see if anything sticks:

Ear plugs or ear defenders to use in busy crowds and during loud things like fireworks. Make sure she has these to hand, so that she has complete control over them, and can decide when she needs to block the world out.

A pediatric wheelchair / SN stroller could be a help to her. Partly it will make it harder for her to bolt; but it will also give her a 'safe place' to go to, and put a bit of a barrier between her and other people. The downside is that she will be lower down, so crowds will feel more oppressive (I use a wheelchair, and tight crowds are really stressful for me).

Make sure she eats regularly. I get more sensitive when my blood sugar is low (as Sue said), but I don't always feel hungry until after I've begun 'stressing out'. Carry some snacks around with you, so you don't get caught short in a line.

Try and check in with her regularly. These things can often be building for a while, and it may be that even she doesn't know it's happening. A quick, quiet conversation on how she's doing, and if she needs anything may just help keep her from boiling over, and let her feel more in control.

Keep her cool and hydrated.

Try to plan 'sensory breaks' into your day, to give her some time and space to wind back down. This could be going into a restaurant for a snack during a quiet time; sitting in an out-of-the-way place for a while; going to the cinema in the back of the Kodak building (Main Street Square, MK); or going to the first aid centre for a lie-down.

Make sure all her clothes are soft, breathable and non-constricting. During a bad patch, a scratchy top can cause me pain, and a tight necked-top can make me feel claustrophobic.

Keep an eye on her in places with strong scents, particularly perfume shops (I can't even go into the one in Paris, WS).

Have some of the retrieval techniques others have talked about (such as tracking devices) to use if she does bolt.
One of the big things that helps me when things are bad, is feeling like I have got control of the situation. I need to be able to block out or get away from the things that are stressing me, or I will just continue to escalate. You may want to arrange a signal with her that means 'Get me out NOW', for use when she's overwhelmed and can't talk. It may explain why she has run away from you before, and why she didn't respond at the zoo when you were calling for her; it may not be that she was deliberately hiding from you, but that she had to get away from external stimuli, and was so stuck inside her own head that she physically couldn't respond.
All of these things are just things that I know help me, they may not do anything for your DD. If anything here doesn't feel right, then it may not work for her; you know her better than I do, so don't be afraid to trust your gut.
I hope some of this helps you guys, and I hope the Disney magic does wonderful things for you all. If you or your daughter want to talk to me about any of this, you're welcome to PM me. This is such a tough thing to go through, and I wish I could give you a simple fix, but you know as well as I do that there isn't such a thing (if there was, I know you would have found it). Please remember that none of this is your fault - you are a wonderful mother who is doing everything that she can for her daughter, in a very difficult situation.
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