In Fat Chance, Jack thought she was hot since he noticed her when she turned her french braid from right to left. Kim seems to be jealous of Donna Tobin since she said to Jack when he said so, "So you didn't notice a 600 pound custodian, but you did notice when Donna Tobin changed her ponytail from left to right!" Jack responded by saying "Okay, first, it was right to left. Second, it wasn't a ponytail, it was a French braid. And third, maybe if that custodian had legs like Donna Tobin, I would have noticed him, too!"
Then in Dude, Where's My Sword, she is mentioned by Jerry, when he explained to Eddie why there was a piece of Pizza on the wall of the dojo, saying that "some guy" saw Donna Tobin come in, and wanted to talk to her without having pepperoni breath."
She has never been shown in the show.