When this quarantine is over, take it to your favorite antique dealer and ask him to fix it. It sounds simple enough, but the fancy parts you describe in the front are sometimes plaster, not carved wood. Care must be taken to not damage the front.

I would even go to a frame shop, they may be able to help you out.

Thank you so much for taking your time to respond to my inquiry! Above are detailed pics of the scrolling decorative wood pieces adorning the top and then pics of the back which is attached on the left side but the entire right side and around to the bottom has pulled away from the frame and the mirror is loose as well. I also noticed their are nail holes where supports would have been attaching the mirror to a dresser or vanity.

P.S. I purchased this from an older woman who is downsizing and she nor I can decipher the message written on the back!

"Marv did this room"?

Marv did something!

It looks like you have two problems: the mirror backing and the loose trim pieces. I'm not sure how to deal with either. It depends on how "original" you want to keep it I guess.

Small dab of wood glue for the trim bits I guess, after you get it all cleaned up? Don't try to fix all the cracks and make it look perfect. Go for Clean, with Character.

To reattach the backing, you'll probably want too pull out the old nails and use new ones in slightly different spots, so with new holes in backing and frame (pilot holes, please!). If the backing is warped, it won't work as well, but you don't want to replace the backing because Marv will haunt you. :)

Maybe instead, use regular mirror clip things, as low profile as you can find, and then loosely reattach Marv's backing. You do want that mirror snug inside if you're going to hang it. I don't know about this, though. I'd probably spend some time browsing in the hardware store which we aren't supposed to be doing right now.

The decorative top is certainly wood! I would glue anything loose.. maybe even with a hot glue gun if you are careful, but most any glue will fix those small loose bits.
And can you glue the back on? If the back is re attached, will that secure the mirror?

Will you varnish it or paint? If varnish ( which i think would be lovely!) b careful about getting glue on parts that will be staine as the stain won't take.

A caution on nailing that trim back on and why the glue would be better is that I have a chair with that same trim. When I tried nailing it back on the wood split even though I was using the same nail and hole. I never was able to find all of the pieces.

Use short, small screws and a washer instead of nails.