4 Answers

This is Milicent Martin on the top. She and Debbie Reynolds (on the bottom) do bear a resemblance to each other.

Just reading through this old question and thought I'd help.  :)

7/21/12 There was a CASTLE rerun on this evening in which Debbie Reynolds made a guest appearance.  I am about 99.999999999999999999% positive it was originally shown in the 2011-2012 season and was definitely NOT the season finale episode. She played the role of a theatre critic who was a "friend" of Castle's mother. 

Since Castle is a recurring series I looked at 2 Bio. pages for Debbi Reynolds...each listed both movies and tv shows Debbi has been in- even if just for an episode or two.  Neither listed Castle.  When I googled Castle there were multiple sites for final episodes- for the dif. seasons.  If you know which season the finale you speak of was in then google Castle and you will be able to locate it quickly.

that was season 4 episode 23 a dance with death and like you I thought it was too but the actress was Millicent Martin, sorry we were both wrong :(