101 Dalmatians: The Series unaired pilot (lost episode of Disney animated series; 1996)
Much like how Disney's Recess originally began production with a pitch pilot that would remain untelevised indefinitely, 101 Dalmatians: The Series was first pitched as a pilot or "demo" to Disney in around 1996 (The Recess pilot was pitched at that time too).
1996 was when Disney's 101 Dalmatians live-action remake film came out. The animated series pilot had to be finished and the actual show had to be started by early 1997.
Unlike the Recess pilot, however, this Dalmatians pilot wouldn't be later remade into an episode of the TV show.
Penny's existence is evidenced by an artist drawing the removed character in a sneak peek for the series (twinned with Recess) in between clips of the pitched pilot, which was released on 1997 VHS releases of 101 Dalmatians (1996) and Doug's Birthday Blues as a promo for ABC Saturday Mornings.
Unfortunately, the clips shown in that sneak peek are all that is known about this pilot.