The moral of this story is...don't believe everything you read on the internet. According to a 4Real friend, the picture I found which was clearly labeled as St. Margaret of Scotland was actually a black and white copy of an illustration of St. Ermengild from Fr. Lovasik's Book of Saints #10.
Both are medieval saints but St. Ermengild lived almost 400 years before St. Margaret. What I find interesting is that St. Margaret is often shown holding a black cross like the picture of St. Ermengild. I wonder if the artist didn't use a description of St. Margaret as a guide for his/her St. Ermengild.
So, I don't know if I should relabel this one or not. Sorry about the mix-up. Just wanted to let you know.