Thanks for all of your opinions. After days of searching the internet (after years of searching the internet) I've come to the conclusion it's a mantilla of some sort. I've found similar species on asian webpages listed as "magic beam" or "potamotrygon sp. ?". She is eating well, readily taking chopped smelt, earthworm etc. I will update pics as soon as I get around to replacing the battery in my camara.