My Desperate Valentine - S2-E16
Other mistake: At the end of the episode Brandon mentions he dropped Emily off with her parents and spoke to them. In season 4 when he goes to look for Emily at her parents' house in San Francisco he asked the woman who answered the door if she was Mrs. Valentine, as if they had never met.
Stand (Up) and Deliver - S1-E17
Character mistake: In one scene Brenda refers to Brandon's political opponent as "Michael Miller" but a few scenes later David refers to the same guy as "Robert." He's referred to as Robert for the remainder of the episode.
Chosen answer: Yes, she was.