A Very Topanga Christmas - S5-E11
Character mistake: When Cory is talking to Alan in the middle of the night, he mentions that Topanga has been staying with them for less than 8 hours. She arrived during the day time, and then convinced the family to go to Vermont to get a real Christmas tree, which they are cutting down at nighttime, and Eric later expressing after the new tree has been put up and decorated that it was 600 miles round-trip. All of this would take more than 8 hours. Driving from Philadelphia to the southernmost part of Vermont and back again alone would take more than 8 hours.
Answer: Topanga's middle name is never specified. Considering her sister's name is Nebula Stop-the-war Lawrence, Topanga's is probably something equally unusual.