Answer & Explanation
Given that If Theresa's daughter is my daughter's mother
It has 2 ways of Answers such that it depends on the sex of me. That is Male or Female.
1) If I am a Male :
My daughter's mother is my wife.
My wife is Teresa's daughter
=> I am Teresa's Son-in-law.
2) If I am a Female :
My daughter's mother is myself.
Myself Teresa's daughter.
=> I am Teresa's Daughter.
But in the given options only Son-in-law is available and daughter is not given.
So, Son-in-law is correct.