Sometimes news has been sitting on the Internet for years waiting for someone to discover it. And today, that has to do with a piece of Harry Potter lore that J.K. Rowling has been talking about since 2000: the fact she originally conceived another Weasely family member who was a Slytherin.
The character's name was Mafalda Weasley and, in early versions of Harry Potter and the Goblet of Fire, she served the role of Rita Skeeter, as sort of Harry Potter nemesis and foil for Hermione Granger. Mafalda was the Weasley kids' second cousin who was staying with the family for the summer before going to Hogwarts. There, she would be sorted into Slytherin, and ultimately oppose everyone.
Rowling first alluded to Mafalda in 2000 when Goblet of Fire was published. Later, she put information about the character on her official website, which then went away in a massive redesign. Though the info is not online anymore, it is on Reddit, and reads as follows:
Mafalda was the daughter of the 'second cousin who's a stockbroker' mentioned in 'Philosopher's Stone'. This stockbroker had been very rude to Mr. and Mrs. Weasley in the past, but now he and his (Muggle) wife had inconveniently produced a witch, they came back to the Weasleys asking for their help in introducing her to wizarding society before she starts at Hogwarts. The Weasleys agreed to taking her for part of the Summer, including the Quidditch World Cup, but regretted this almost immediately. Mrs. Weasley suspected that Mafalda's parents simply wanted to get rid of her for a while, because she turns out to be the most unpleasant child Mrs. Weasley has ever met.
Mafalda was supposed to convey certain information about the Death Eaters to Harry, Ron and Hermione, because as a nosy, eavesdropping Slytherin who likes to impress, she does not keep her mouth shut when she overhears their sons and daughters talking. Unfortunately, however bright I made her, there were obvious limitations to what an eleven-year-old closeted at school could discover, whereas Rita Skeeter, whom I subsequently built up to fulfil Mafalda's function, was much more flexible.
The best thing about Mafalda was that she was a match for Hermione. To the latter's horror, Mafalda was highly gifted and a real show-off, so that Hermione was torn between deploring the rule-breaking and longing to join in and beat her.
Now, Mafalda is a not really a character at all. She's a concept. An idea Rowling had and discarded, making her nothing but a footnote in Potterlore. But a very interesting one to be sure.