Well now, this is interesting--I'm just back from viewing the re-make of "The Wicker Man", which stars Nicholas Cage, Ellen Burstyn and Leelee Sobieski. In the new film, Cage's character is lured to "Summersisle" by a letter from his ex-fiancee, who just happens to be named--wait for it--WILLOW! The character in the original film was played by a very pregnant Britt Eckland, and was quite different from the character in the new film. I wonder if JW might have seen the original, and thus "lifted" the name from there.
BTW, for those interested, I don't feel that the re-make is quite up to the level of the original, which was quite startling for its time (1973-74). Edward Woodward (playing a virgin policeman!!!!) and Christopher Lee (as "Lord Summerisle") were both excellent, and there was much more focus on the ancient Celtic roots of the earth-based religion of the island's inhabitants. The new film turns the story into a Witches/Wiccans vs. "Normal" People tale, the sort of thing that has been done to death many times before. In any case, it's worth seeing
both versions for comparison. :-)