Yi (Viet)
Replies
There are too many factors with Vietnamese to provide a concrete answer without the spelling or precise audio, though I am certain that "Yi" is not the correct Vietnamese spelling as it doesn't match the orthographic rules. Also, do you know if your friend is using the native order for her name (surname-given name) and not adapting it to the Western order?
Vietnamese is also a tonal language (with six tones), so tones completely change the meaning of words. Even with the tones, there are many homophones as well as some significant differences in dialectal pronunciation. With this in mind, even "Trinh" might not be correct, though it does seem a good fit.
But my best guess (assuming that she is using native order) is that the surname is Dư (IPA in southern dialects: /jɨ/). This surname comes from Chinese Yu (余) which you can read about here: https://www.ancestry.ca/last-name-meaning/yu
Vietnamese is also a tonal language (with six tones), so tones completely change the meaning of words. Even with the tones, there are many homophones as well as some significant differences in dialectal pronunciation. With this in mind, even "Trinh" might not be correct, though it does seem a good fit.
But my best guess (assuming that she is using native order) is that the surname is Dư (IPA in southern dialects: /jɨ/). This surname comes from Chinese Yu (余) which you can read about here: https://www.ancestry.ca/last-name-meaning/yu
Update: It's spelt Y
That seems correct! She is from South Vietnam.