This was a total surprise. I was at the offices of The Korea Times in Seoul earlier today doing some research into the 1969 hijacking of an airliner by North Korea (that's one of the articles I photographed) and also some violence committed in 1999 by one of the many cults Korea has produced when I stumbled upon a Williams article about his work on The Phantom Menace. Interestingly, he mentions Princess Leia's Theme, but it sounds like he just meant that some of his original trilogy themes make brief appearances and not Princess Leia's Theme per se - "Princess Leia's Theme or whatever". Yoda's Theme and an obvious quote of Darth Vader's Theme do make the briefest of appearances in "The Queen Confers" just before the end.
But is it possible there is also a brief Princess Leia quote in the unreleased/unused material? Perhaps in reference to her mother? Probably not...
It's an AP article, so it's probably been seen already by some here, but here it is again.... 1999, when Williams was 66 and still very much a youngling.