It almost looks as though she was attacked at some point by fire ants. Staph infections also look like that, but usually it's small red pustules and draining.
Fleas didn't help the situation either, I'm sure. Poor thing.
Maleseb shampoo would probably be good to bathe her in if you have any. It's medicated for fungal/bacterial skin infections and sure wouldn't hurt her.
I'm so thankful you have her now and treated her!!
Keep us posted on how she's doing and hope if you're not keeping her, she gets a great home. She's a doll, and you are wonderful for taking her in and taking care of her!
Sure wish someone would've taught those kids to be as kind hearted.