What is the correct pronunciation of the given female name "Gillian"? J.C. Wells' Longman Pronunciaiton Dictionary gives only the form /?d??l i??n/ (as in "ginger"), on the other hand I've heard an interview with David Fincher, who pronounced the name of his screenwriter /?g?l i??n/ (as in "get").
Jill, of fetching water fame, has a sound equivalent to the soft 'g'. Gill, as an anatomical feature on a fish (ghoti), has a hard 'g' sound. With that being said, many rules are ignored when it comes to personal names (and often times in English).
There are no rules on how to pronounce people's names. They're the only ones who can tell you.
For what it's worth. I know two females named Jillian with a J. I look at that as the correct spelling.
To expand on Peano's statement, there are no rules on how to spell people's names. I have known Gillians of both pronunciations. And I have a grandson whose middle name is Mathew. I gently protested, but was overruled. Not my kid, not my decision.