RIDDLE: If Theresa’s daughter is my daughter’s mother, what am I to Theresa?

Of course theresa

It is theresa daughter  because  Theresa daughter,your daughter's mother  you are the mother of the daughter  and the daughter of theresa is your daughter's mother You are your daughter's mother that means you are theresa's daughter

It's obvious it's theresa

i am Teresa"s daughter    

Of course it is Teresa because because Teresa is her daughters mother