This is what eventually became Mewtwo Strikes Back. As we know the Pokemon series was originally scheduled to end at Kanto, it was only late in the series when they realized they had a huge hit that it was continued on into Orange Islands. Apparently, and I am unsure about this, this short was supposed to be the book end for the original series in Kanto. With a adult that looks like Misty, and her daughter meeting up with Pikachu.
Pokemon the first movie was suppose to end the series, the video below
shows misty as an adult with her child.
https://www.youtube.com/watch?v=b70GRNYnacI
You could just join us in the Pokethread (we're v fun!)
Though the show has been pretty awful, the original was absolutely amazing.