Your mirror is from the Victorian period; more than likely 'late' Victorian. How many inches tall is it? During that era of time, ladies vanity sets were very popular. Generally in the set was a mirror, comb, and brush, all matching. The more expensive/larger sets had perfume bottles, 2 different sizes of mirrors as well as more combs, etc. If you GOOGLE Victorian vanity sets, you'll see lots of photos of this type of hand held mirror.
Some of the sets were sterling silver and others were plated. You can buy an inexpensive acid test kit online(ebay) or either take it to your local pawn shop for them to test it. They will test it free if they think you're interested in selling it for silver melt.
Neat find, Breezie