If you take a look at Sagatorel's other comments he seems to have issues about British nationality especially the English. Some of them almost to the point of being xenophobic (if not racist). So I would treat what he says here with a a pinch of salt (if not a massive bag full).

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I've not read in any media interview Naoko has done that she is 'ashamed at being thought of as English'. She speaks English with a perfect home counties accent and worked here (UK) on stage and TV for most of her career so why would it be ' shameful' that people who didn't know any better would think she was born here?
The only part right is that she has said she wants to do more theatre work at some point with the previous company she worked with in Japan.

Can you cite a source for this? I'm guessing no.

She said she was tired of the show and ashamed people still wrongly confuse her as english. She is Japanese and want to do more work in Japan.

No, she has left the show, unfortunately. She did an interview where she said they had discussed the possibility of her returning in some way or another, but that she would only do it if it was well-written and for the right reasons. So never say never but I doubt she'll be back next season.