Can anyone answer this riddle because I can t get my head around it?

You are Teresa.

Teresa ... Teresa's daughter ... Teresa's daughter's mother

i tried but my brain exploded

-Her Husband. :)

daughter or son-in-law

"Teresa s daughter is my daughters mother"
T-> D -> D
.......Me->D
that is Teresa is your mother you have a daughter
or you are married to Teresa's daughter and had a daughter with her

you are Terasa's daughter

"My daughter's mother", thats you

so if you are "teresa's daughter", that means Terasa is your mother and you are her daughter easy.

Mother Teresa had no children even though she was a mother

Son-in-law

Her daughter.