harry potter - What was the flaw in Goblet of Fire?

From this 2000 interview with JK Rowling:

Q: You mentioned something in a recent interview about a flaw in Book 4. . .
A: Did I? Oh yes. . .I repaired it! This is why Book 4 nearly caused me a nervous breakdown - because for the first time ever I lost my careful plot - which I've had since 1994, I think. I really should have gone through it with a fine toothcomb before I started writing and I didn't. I had a false sense of security because all my other plans had held up so well. So I sailed straight into the writing of Four, having just finished Azkaban. I had written what I thought at the time was half the book - it turns out now to have been about a third of the book - and I realised there was this big hole in the middle of the plot and I had to go back and unpick and redo. That's part of the reason it's longer than I thought it was going to be.

Q: Can you say what the flaw was, or would that spoil things ?
A: No, because that would ruin it.

Now that HP and the Goblet of Fire has long since been published, has JKR ever revealed what this "flaw" was and what she needed to do to fix it?

Answer

I thought about this issue too and researched some time ago. I found half of the answer but not the whole one. So JKR told us in BBC Newsround, 7/8/2000 interview there are two plot holes.

The famous plot hole. I got halfway through my plans and realised there was this huge gaping hole in it, there's two - it just didn't meet and that was entirely my own fault, I should have had the good sense to go through it very, very carefully before I started writing but I hadn't.

So I'd written what I then thought was half the book it turns out to have been a third of the book before I realised that this wasn't going to work, so I had to do an enormous amount of unpicking, and in the unpicking process I'm afraid the Weasley got [draws finger across her throat]

First part is Ron's cousin Mafalda Weasley, it was explained in this interview. Ginny was supposed to be first girl born in the Weasley family in several generations.

You sat on the title for a long time, too.

JKR: The title thing was for a much more prosaic reason: I changed my mind twice on what it was. The working title had got out – 'Harry Potter and the Doomspell Tournament.' Then I changed Doomspell to Triwizard Tournament. Then I was teetering between Goblet of Fire and Triwizard Tournament. In the end, I preferred Goblet of Fire because it's got that kind of “cup of destiny” feel about it, which is the theme of the book.

Was this the hardest book you've had to write so far?

JKR: Easily.

Why?

JKR: The first three books, my plan never failed me. But I should have put that plot under a microscope. I wrote what I thought was half the book, and “Ack!” – huge gaping hole in the middle of the plot. I missed my deadline by two months. And the whole profile of the books got so much higher since the third book; there was an edge of external pressure.

And what exactly was that gaping hole all about?

JKR: I had to pull a character. There you go: “the phantom character of Harry Potter.” She was a Weasley cousin [related to Ron Weasley, Harry's best friend]. She served the same function that Rita Skeeter [a sleazy investigative journalist] now serves. Rita was always going to be in the book, but I built her up, because I needed a kind of conduit for information outside the school. Originally, this girl fulfilled this purpose.