The 30-year-old star announced she was leaving the E! series last week just days after co-host Giuliana Rancic was forced to apologise for making an offensive remark about Zendaya Coleman's dreadlocks at the Oscars last month, but she reportedly hasn't been happy on the panel without her pal, who died six months ago.
A source said: ''After Joan died, Kelly gave [the show] a shot.
''Kelly thought the show was going to be revamped [after Joan's death], but it was basically the same except they hired new people and there was a new set.
''[The show] has gotten a little better, but it's not what she wanted.''
The purple-haired fashionista feels the move is a ''natural progression'' because some on the show have reportedly been ''miserable'' in recent weeks.
Another insider added to PEOPLE magazine: ''There was very little direction. It was almost a trial by fire.
''People thought bringing Kathy in wouldn't be as big a deal, but she did things differently. With Joan it was a well-oiled machine. People were miserable before this [Zendaya incident] even happened.''
Meanwhile, Kelly is reportedly ''fuming'' over rumours Khloé Kardashian could replace her on the programme.
The 'Keeping Up with the Kardashians' beauty entered into talks to join the E! series after Kelly announced her departure last week, but the outspoken star isn't happy with the ''buzz'' surrounding Khloe's possible appointment.
A source close to the former co-panellist told Star magazine: ''Kelly is fuming over this. She'd never admit it if she were forced to quit, but the buzz surrounding Khloé coming on board makes her wonder if E! was just waiting for a reason to push her out.''
American Thighs was released on this day in 1994.