What Could Have Been: J.K. Rowling intended to put in a female character named Mafalda (not the Ministry of Magic employee). She was written at being a "black sheep" cousin of the Weasleys'; extremely badly-behaved, unpleasant to be around, nosy and loose-tongued, and to top it off, being sorted into Slytherin. In addition, she would have been the first rival to Hermione, being equally brainy and a show-off, and eavesdropping into the conversations of her fellow Slytherins hoping to relay and impress The Trio. Despite Rowling's fondness for the character, she was ultimately axed due to her age limiting her story potential. Rita Skeeter was thus created to fill the nosy, eavesdropping role instead. Mafalda would be the daughter of the accountant relative Ron mentioned to Harry in Harry Potter and the Philosopher's Stone.
Write What You Know: At the height of the Religious Controversy for Harry Potter, Goblet of Fire in particular was heavily criticized for the religious imagery of Voldemort's resurrection. Considering Rowling herself is actually a Christian, the imagery was definitely intended.
Rita Skeeter's presence in the story is said to have been based on Rowling's own experiences dealing with fame and reporters.