Flip-flops = chemical burn?

My mom would say, "This is why I didn't let you wear cheap shoes as a child."
http://www.lamanaphotography.com/walmart2.htm

Pictures are quite graphic, so if you're easily grossed out, don't bother with the link.
Basic premise is that $3.00 flip-flops from Wal-Mart gave this woman massive flip-flop shaped chemical burns. The burns are taking a long time to heal and have caused her serious pain. She's not allergic to latex or rubber, so it's more likely that there's some toxic chemical (aside from the petro-chemicals probably in the shoe bottom...) in the "thong" part of the sandal. She tried to get Wal-Mart involved and has been shot down.