Correction: This was the PRE-pilot. Yes, it sucked so much it didn't even get a full pilot. This was Will Dozier's 2nd attempt to recreate the magic of his Batman show. Unfortunately, his unwillingness to repeat himself led to the deathly humorless Green Hornet and...this.
I think they were trying to show you that she sees herself as more beautiful than she is.
Two problems: a) the woman acting as the reflection wasn't mirroring Wonder Woman's movements (they both moved their left arm at the same time, etc), so it looked even cornier and b) the woman in the mirror wasn't so much more stunningly beautiful that you got the "Julie Kavner thinks she looks like Linda Carter" gag that they were trying to go for.
One single point in this trainwreck's favor: a live-action Wonder Woman whose butt isn't as flat as a pane of glass.