Either way, it's a modern name, so no biblical links ... I don't know why it would come up in a Catholic book as there isn't likely to be a St Geralyn ... maybe they just didn't think there was a
Demon Geralyn either, so it was safe!
Gerald, made feminine by adding -lyn, is how it was done.
Lyn, like
Ann, was vey popular both as a first name, a middle name and a name element; as you say,
Carolyn suddenly became a version of
Caroline. I think it's a pretty name, nicer than
Geraldine for sure, and much less common than
Michelle or
Michaela. Your parents did a good job!