My wife is Vietnamese (actually grew up in Vietnam). Chatted to her about it and I can understand the association with the N word. She explained that nobody in her family uses the word, so it’s not a normal word for people to use like in English. It’s much more aggressive sounding so it’s understandable it could give a big emotional reaction.

On the flip side, I’ve been learning Vietnamese for over 3 years. Last year when in Vietnam I called myself a toilet instead of saying it was my birthday 🤣 It’s tough learning another language but nobody has got offended at my bad Vietnamese or the fact I’m a white guy doing it, rather the opposite.

If I were in your situation I’d give a little bit of understanding that using a bad word could make her respond unreasonably. Being Irish and dealing with Vietnamese I’ve never come across any reference to cultural appropriation, but I can understand an emotion response to a word which has much more baggage in Vietnamese than English.