There is a complex relationship between many Asians. Many move to Japan for a better life quality. The Japanese have done some atrocious things in the past. To be honest with you, she's allowed to feel however she wants about anything. Many multi-ethnic people have severe displacement. You can look one way, be cultured another, and have several other things. I bet you fifty bucks she does a shitton of cute stuff that is tied to her actual culture.
I am ethnically Japanese, but I am culturally American. Among other things. There are bits and pieces that have dripped through, because my family has sustained its own culture.
You will never understand the hatred, it's not worth trying. Also stop being a dick on the internet. And probably real life. But more so on the internet. People's sufferings are not something that need to equate to be worthy of sympathy (at minimum).
It's an older mindset, what you're referencing. But many Americans did actually have quite the problem with people they fought against. Some still do. Also, there can be many facets to ones identity. She may be ethnically one thing, but culturally she isn't. Everyone does fucked up shit during wartime, it's why we don't want wartime. This is true.
The last comment was weird, but I also have lived it so much that it's just...ugh.