Mrs. Katswell is Kitty's mother, who first appeared in a flashback in Operation: Happy Birthday. She somewhat resembles her daughter, with her '50s hairdo.
There is not much known about Kitty's relationship with her mother, but in Diary of a Mad Cat it appears Kitty isn't that close with her. Mrs. Katswell seems to be upset with Kitty for never calling her on her birthday and would compare Kitty to her pretty sister, who is in jail. She even bothers Kitty for being single.