British girls don't cry: that was J.K. Rowling's motto as she stood up in a New York court on Monday, defending her stratospherically-successful seven-book Harry Potter series from the claws of a “former fan”. “These characters mean everything to me,” the 42-year-old multimillionaire said, admitting that she was struggling to keep her upper lip stiff: “I really don't want to cry because I'm British.”

This moment of courtroom melodrama was sparked by Steve Vander Ark's plans to publish a Harry Potter Lexicon - a “rip-off” reference work that Rowling damned with accusations of “utter laziness” and “wholesale theft”.

Last year, Rowling announced her own plans to produce a Harry Potter encyclopaedia, a work that might take ten years to complete - and, crucially, the proceeds of which would be donated to charity.

If Joanne Rowling did break down and blub, it wouldn't be the first time. Her fairytale ascent from single mother on benefits, scribbling away in secret, to global phenomenon responsible for more than 325 million book sales and billions of dollars of film revenue, is well documented - and she has been honest about the emotional wobbles along the way. Now happily married with three children and properties in Aberfeldy, Edinburgh and London, she recalled earlier, unhappier times during a TV documentary screened last year. Returning to the tiny Edinburgh flat where she had grappled with the ending of the first Potter book, Rowling burst into tears: “Coming back here is just full of ghosts,” she sniffed.

Writing itself has proved a tearful experience: she wept when composing the death scene of Harry's godfather Sirius Black and, drawing to the end of the final book, found her “euphoric and devastated . . . in a hotel room on my own, sobbing my heart out”. Smaller upsets have known to set her off, too - when her son was born, a company sent her free Babygros: “I got quite tearful at one point. I remember if someone had given me free Babygros [when her first daughter was born] that would have been a very big deal.”

It's her Potter-party, and she'll cry if she wants too. But it's not all self-pity, and Rowling is careful to avoid the sympathy black-out that sometimes affects the rich and famous: “We all know I've made enough money. That's absolutely not why I'm here,” she told the judge this week. In fact, she has donated hoards of cash to a range of charities (some of which she set up herself) serving one-parent families, neglected Eastern European children and multiple sclerosis sufferers, as well as raising millions for Comic Relief from the sales of Potterphenalia.

Rowling's Britishness might prevent water-works in the courtroom - just - but she needn't worry: her reputation is so spotless that a few salty tears couldn't stain it.

Explore Books

• Book Extracts

• Book Reviews

• Books Group

• Audio Books

Times Recommends

• The 100 Best Books of the Decade
• The Times picks the 50 best paperbacks of 2009
• The conversation: James Ellroy