If Teresa’s daughter is my daughter’s mother, what am I to Teresa?
It’s tricky and took us a while to get, but the answer is… Teresa’s daughter!
If you think about it, the phrase “my daughter’s mother” could only apply to you. If you’re a female (which you are in this case), “my daughter’s mother” could be replaced with the word “me.”
Then the phrase would read, “If Teresa’s daughter is me, what am I to Teresa?” Therefore, the correct answer is Teresa’s daughter.