OK. Now I saw it. My PBS affiliate wasn't working at the time, but at least I found it at pbskids.org. It must have been a promo or something that I saw before.
I thought that it was pretty good, but I agree that Abby's presence really made no sense, so why they wanted to use her there rather than her stepbrother Rudy who really is a monster is beyond me. At least Oscar's presence as the cab driver made more sense since his appearance was more of a cameo rather than him being essential to the "monster" plot.
It's kind of an interesting take about Cookie, Elmo, etc. also being the monsters at the end of the story. They probably should have called it, "The Monsters and Fairy at the End of this Story," but I guess that would have given too much away.