Two suggestions: first, you could go through Illusion Jewelry's database page by page to look for this mark. It looks like the site categorizes marks by the manufacturer's company name only. If "MARIANNE" is one of several lines offered by a company with a totally different name, it wouldn't show up on the page of manufacturers starting with "M".
Second - you might look for a forum specializing in costume jewelry, and post your questions there. We PS'ers appreciate jewelry of all sorts, but you're more likely to come across someone who recognizes this mark in a community that specializes in costume jewelry.