You could go around it with door trim
Hi Jeri. I'm Cindy. Frame this tall mirror. Take a walk thru the trim department of your local home important store. Pick out the best trim that appeals to you. For the corners, use rosettes or cut the trim with a 45 degree angle. Use finishing nails and wood glue to hold it all together. Put a tiny amount of wood putty in the hole the nails make. After it's dry, sand it with a fine grit sandpaper. Then prime and paint or stain it. Wishing you all the best.
here are 4 ways to frame a mirror https://www.charlestoncrafted.com/2018/03/20/four-best-ways-frame-mirror/