In a word, plump. In two words, morbidly obese.

Mrs. Johanssen has a weakness for chocolate, and presumably every other rich, edible substance. She is also hypoglycemic and subject to fainting spells following strenuous exercise, like climbing a single flight of stairs. Daria and Jane show up at her door to sell chocolate, but after she faints in front of them, Daria refuses to sell her any, as the chocolate might kill her. Jane has theorized that Mrs. Johanssen ate her own family. She may be right.

She meets the Fashion Club while they are collecting clothes for the homeless, but they decide they don't actually want any of her clothes. She tries to stop them from leaving, hoping that perhaps they might be selling chocolate. She also encounters Daria and Jane at a later date (but fails to recognize them) when she comes to the flea market and asks where the "Snow Domes" are.

Mrs. Johanssen eventually receives psychological therapy from Dr. Millepieds at the Quiet Ivy retreat. During her session, she suggests that she does use food as a means of comfort, and that she harbors resentment over being called an "accident", presumably by one or both of her parents. When Quinn interrupts their session, Mrs. Johanssen becomes more interested in Quinn's suggestion of vertical stripes for slimming than anything her doctor has to say.

Mrs. Johanssen suffers from occasional seizures as well as fainting spells, and has been warned by her doctor not to exert herself suddenly.

She shops at PayDay from time to time (presumably because they offer food in bulk) and engages in fierce competition with DeMartino for free sample cheese logs.