You mother's sister is your aunt, but a god daughter does not have to be a blood relative. If that's the case, there's no special word for what you're doing.
Niece. Your mother has children, you and your sister. So your mother's daughter is your sister. When she has a daughter, this is your niece.
cousin
Mothers sister is aunt and son is cousin so daughter wouldn't that be a niece
no....because she is a sister for you
Sister, but possibly only half sister if the baby and the father's other daughter have different mothers
Your brother or sister's daughter is called 'your niece.'
Your sister's daughter is your niece.
Your sister's daughter is your niece. You are her aunt (if you are a woman) or her uncle ( if you are a man).
niece
...niece.
Such a person would be your second cousin, and in most places marriage between second cousins is legal.
The relation of the mother;s sister to daughter is niece-aunts.