Valerie Harper's return to television in the mid 1980's was a huge success. Cast as the mother of three boys, Ms. Harper saw her show's ratings increase in its second season, a rare thing to happen in television. She thought that since the show was called Valerie that the network would have to do whatever it took to keep her happy, so she asked for a substantial raise.
Ms. Harper totally overestimated her power over NBC. The network resisted her demands, though it eventually capitulated and she reported for work. After filming just the season premiere, however, Valerie went AWOL again, making more demands. NBC had enough and fired her, with Sandy Duncan stepping in as the boys' aunt. Valerie was killed off. The show was originally re-titled Valerie's Family, but the threat of lawsuits made NBC change the title to The Hogan Family, a title that is now used on all episodes of the show in syndication.
Afraid of further lawsuits from Ms. Harper, NBC had the show producers write in a fire that would destroy the entire house, including all pictures of Valerie Harper's character. This would explain why the family had no pictures of her in subsequent episodes.
