I need to translate these words for a rather formal circumstance(Visa interview). And I am referring to serious relationships, not just something like "sugar daddy", and I think it worths to mention that I am not talking about "养母","养父","养子".
"Godmother","Godfather" and "Godson" are the first showing up in my mind, but in China these words seem irrelevant, and I am afraid if I use these terms I would be required to provide some documentation(I guess these documentation exists in a literal "Godfather/Godson" relationship in western/catholic countries), which I don't have.
So, is there any better translation for "干妈","干儿子", etc. that can help a Visa officer understand the relationship?
P.S. I need to write an "invitation" letter to her, and I am trying to fill this blank at the very beginning: Dear ______, so descriptive terms like “close family friend” won't work. Based on everyone's answer, I guess maybe her name would be the best to be filled in. But that seems a little absurd in a Chinese environment.