We have something similar. There are issues with certain things in the outside world that discourage him, but fundamentally I think he just likes being at home as it's very familiar and he has everything he wants.
I was on a course where I was told that there has to be something in it (going out) for them, and it is so true.
Although conventional parenting techniques would probably frown upon effectively bribing your daughter with a mcflurry, I don't think it's necessarily a bad thing to do in this case, for the time being. Having regular mcflurrys is better and healthier that being a prisoner in your own home. The more she goes to a particular place the happier she will probably be to go back, and just generally getting into the habit of going out will make going anywhere easier. If you get her out the door by saying "let's go to McDonald's" can you then get her to go on somewhere else afterwards more easily? Or would she respond to going to place X then going for a Mcflurry? You may then find something or somewhere else that she feels is worth going out for so it won't always have to be a mcflurry. Is there anywhere connected to her special interests that she'd be happy to go to? Again, with the aim that you can get her to other places before/afterwards or at a later date once she's more familiar.
Does putting a photo on a calendar of where you are going to go on certain days help?
How about drawing the sequence of things you are going to do that day so she can see exactly when you are going out and coming back. It might make her feel more secure.
I often show my son videos and/or photos of somewhere before I even mention going.
I get him to think it looks good first then mention that we might go there soon/one day. Once he's put up his barrier and decided he doesn't want to do something it's practically impossible to convince him to go.
I'm just brain splurging in no particular order, sorry if it's unstructured, or if I'm teaching you to suck eggs.
I've heard that returning home as soon as your daughter asks (and letting her know this is what is going to happen) will build up her confidence that you will look out for her. For a while she will test it and you will stay somewhere for 5 mins or not even get there but after a while she should hopefully start to trust you, if becoming overwhelmed when she's out is an issue.
Can she carry a fly swap, so she feels in control? Or a backpack full of sensory things/distractions for difficult moments. Headphones and music/stories/relaxing sounds so she's out but doesn't have to engage with the world?
If she's really anxious possibly try re-exposing her gently. Maybe use a visual timer. Agree with her in advance that you're going to try being outside/being somewhere for X mins (very low to start with) and build up. Explain it will be hard but Praise/reward her efforts.
I hope you get somewhere. It is so frustrating when you know they are being their own worst enemies.