Name change

The same reason why most every other actor/actress changes it: to create a more unique or creative stage name. They are in the movie industry after all.

I thought it was because where she is from everyone pronounces it Ginnifer and when she moved people pronounced it Jennifer and that wasn't her name. Therefore changed it to how it was pronounced.

It might be because of SAG rules. Only one person with the name "Jennifer Goodwin" can be registered with them, so she changed the spelling in order to register. Julianne Moore is one of the biggest examples of this: she couldn't register as Julie Smith, Anne Smith, Julie Anne Smith, or even Julianne Smith. So she's Julianne Moore.

there is a David Letterman interview in which she explains how she is from "mimphis Tinnisee" and writes with a "pin" and her name is pronounced Ginnifer. when she moved to New York and her teachers called her Jennifer she didn't realise they were talking to her and they would only say Jennifer not how she knows it as and when she spoke to her mum, her mum said "you're a southern lady, your name is Ginnifer" and so she changed the spelling phonetically. her nickname is also Ginny which would confuse people if it was like Jennifer nn Ginny