Name Change Records?

[Reece Morris]

I am looking at Marriage Records for my grandparents, and I have found one. The details are ALL correct, right down to the middle names, except that my grandmothers name is spelled Jillian, rather than the one on her gravestone, Gillian. Is it possible that she could have just chosen to use a G instead of a J and nobody thought to check? Or would there be a record online somewhere of a change? Perhaps she could have changed it when she took my grandfathers surname?

Any help would be insanely helpful!