What chapter in the Deathly Hallows made J.K. Rowling break down in tears?

JKR in her interview with Meredith Vieira:

"I really, really, really cried after writing Chapter 34, which is where Harry walks back into the forest for what he thinks will be the last time … It was because I had to live that with Harry and feel the weight of his disillusionment and his fear because he believes he's being sent to his death by Dumbledore who he saw wanted to keep him alive. So that was massively moving to me to write. "

It was chapter 34, The Forest Again, she cried because Harry had to sacrifice himself to defeat Voledemort.

I know you don't want think kind of answer but I believe she said it was the chapter where Harry is walking into the forest thinking he is about to die. If you find the today show and dateline interview with her, she says it then.

I saw a televised interview with Meredith Viera, where she said it was chapter 34.

She is quoted in beyondhogwarts.com as having cried when Harry realized he had to sacrifice himself to destroy Voldemort and he was walking into the forest to do so.

It had to have been the one where Harry was walking to his "death" and he called up his family from the dead. Definitely the saddest chapter, even though *spoiler*

Yes, you should check out her website, it has all sorts of information including biographical about her!