If you have a basin or some kind of tub, a good soak is probably going to be easier on her than you trying to wipe or scrub her with a washcloth, since you can't see what's under there. The water only needs to be deep enough for her to sit in and she should tolerate it fairly well. Try to soften...
@micstrachan, do you think it would be a good idea to give her a warm-water soak and see if she can get that crusty stuff off? Maybe put a little Dawn dish soap in the water?
Maggots look like white rice that wiggles, they are fly eggs. Not eggs, larvae, sorry. I can't see any in those pics, but I'm not looking at her in real life. Is that something crusty in her bottom? Does she look impacted?
When is the last time she looked okay to you? Just check to make sure you're not dealing with a case of flystrike. That might account for why she's pecking at herself. If that's the case, you need to try to get any maggots out of her ASAP, they are literally eating her alive. Let me tag a helper...
Hi, Lauren. Since you are going to be separating her anyway, she won't need the apron. Can you take it off and give us clearer pictures of her wounds? If possible, separate the feathers so we can see actual skin. Thanks.