First off, congrats on the rescue your cousin made. Always great to hear that a mistreated animal is in better care now.

So far, your setup sounds about perfect. I wouldn't mess with those, and just concentrate on leaving the snake be to get settled. She's been through a rough life, it seems, so it will take her a while to realize this is what it SHOULD be.

Offer a prey item slightly smaller than her girth, just until she becomes an established feeder, then you can upsize. But wait a week or so, to let her settle, before offering any more food. It will only stress her out more, the more often you try. Is she emaciated, noticeably skinny? The only time to worry about force-feeding is if the snake looks like a bone rack. Force feeding is very stressful, and is only useful to keep it alive, not happy.

As for the burn, the only helpful thing you can do, if a vet visit isn't necessary, is to put some neosporin (without painkillers) on the burn. This will soothe it and help it heal faster.

Good luck! Hope to see some pictures soon.