Answer
(c) Daughter.

A guy, when he says, “My daughter’s mother”, he is referring to his wife.

A lady, when she says, “My daughter’s mother”, she is referring to herself.

Based on the options given, we can safely assume that it’s not a guy – there is no option for son, father, grandfather, grandson, etc.

So, when a lady says, “My daughter’s mother”, she is actually referring to herself (or ‘me’). And, if we rephrase the sentence, it becomes, “If Teresa’s daughter is me, who am I to Teresa?”