I've heard this, too, but I'm not convinced. The name is purely English as far as I know. Your Scandinavian DNA makes sense in the context of an English heritage - it was the Vikings, you know, who contributed that DNA. Isabella is in fact a Spanish name (remember the queen?) so the Spanish roots could be there if Isbell is really an Anglicized name.
DNA goes back for thousands of years. Isbells can be traced in England for hundreds of years.