On Wednesday, July 9, 2014 2:53:01 PM UTC+1, S Viemeister wrote:
Cut a piece of cardboard or paper (newspaper works for this) to the size
of your mirror; move it around until you or your other half approves.

Tape it in place, go away for a while, see if she still likes it when you
return. Once you're sure, mark the corners in indelible ink and get her
to sign and date them. Photograph it with a witness.

There, I corrected it for you. :-)

Owain