I don't know. And it's too late to ask my parents.
If I'd been an Elizabeth it would have been obvious why.
So I google famous Susans and find that many - Susan Hampshire, Susan Sarandon, Susan Sontag - are roughly my contemporaries. Their parents responding to the same zeitgeist no doubt.
So, Susan Hayward perhaps? Looking unbelievably glamorous and at the height of her career the year I was born. Google tells me "By the late 1940s, the quality of her film roles had improved, and she achieved recognition for her dramatic abilities with the first of five Academy Award nominations for Best Actress for her performance as an alcoholic in Smash-Up, the Story of a Woman (1947)" I wonder if they'd seen the film beforehand whether my parents would still have chosen her name?
And I wonder if my parents realised what they were giving me along with my name? Susan is the sensible one. The older sister. The one who looks after the others and makes sure they have their scarves and have had breakfast. She's there in the Narnia books (until she becomes too grown-up and sensible to take part). She's the same in Swallows and Amazons. I never identified with the Susan in these stories. I wanted to be a Lucy, or a Nancy, or a Jo from Little Women. The one who was always being naughty or rebellious and getting into trouble.
So I tried to cast off my sensible mantle and became a "Sue". And from then on the only person who called me "SUSAN" in a certain tone of voice was my mother.
But here, in France, "Sue" does not work well. The sound is too short, too abrupt. The combination of letters does not suit the French tongue and (I suspect) is not pleasing to the French ear. So I have rediscovered my full name. But now it has quite another quality.
Asked my name, I say "Susan", but what is written down and what is said back to me in French is "Suzanne", the voice lingering on the final syllable with even a hint of an "a" on the end. Oh, how much more exotic and exciting and mysterious.
Leonard Cohen's Suzanne would never have been described as "sensible".
Narnia books - C S Lewis
Swallows and Amazons - Arthur Ransome