For Love and Apartments - S7-E2
Other mistake: When Cory is trying to get Topanga's parents to reconcile, Topanga's mother mentions to her ex-husband about the "beautiful child they've made." Given that she says "child" in the singular, this can only refer to Topanga. However, the season 1 episode She Loves Me, She Loves Me Not established that Topanga had an older sister named Nebula. So the mistake is that either the show is acting like a character that was firmly established never existed, or Topanga's mother doesn't realise she has at least two children. (00:15:32)
For Love and Apartments - S7-E2
Character mistake: When Shawn is scolding Topanga for getting angry with Cory for travelling to Pittsburgh to try to get her parents back together, he mentions that he travelled a hundred miles to do so. Philadelphia is roughly 300 miles from Pittsburgh. Travelling only 100 miles westward from Philadelphia would barely get them past Hershey. (00:17:53)
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.