Sometimes it can be just a short piece of string from a feed bad, even a feather - seen that one time in a thread, a feather footed bird somehow had a feather that wrapped around the leg and became embedded. Seen human hair get wrapped around a little chick's leg. All these things of course are accidental and can be very hard to see, so I don't mean to imply that if something is wrapped around her leg it was intentional.
Let us know how she's doing. If nothing else, hopefully the soaks and daily care will promote healing, and she'll recover quickly. I'd allow the scabs to fall off naturally, if possible, while it's tempting to pry or pick them off, I've found that it's usually best for them to come loose on their own.