Errr.. about that
https://en.wikipedia.org/wiki/Adeyto She is Twintelle's VA.
Okay, so after a bit of searching, I'm still not sure she's actually a native French speaker. Scratch that: she's not, at least as far as her accent and pronunciation go. I don't know if she can actually speak since I can't find any footage of her speaking French though.
Yes, she's born in Strasbourg, and one of her parents is French, but it doesn't say where pr how she grew up, she speaks only in English and Japanese on her channel - her accent in both languages doesn't really sound like that of a native French speaker anyway -, and her pronunciation sounds kinda weird when she sings in French. Heck, one of her songs is titled "Temptation de l'Ange", which is not how you would write "tentation" in French in the first place. Heck, you'd think an accomplished international artist like her would have a French wikipedia page at least if she was French, but she doesn't.
Not to take away any of her accomplishments, mind you. Just saying that she might still not be French. She definitely doesn't sound native to me, from what little I've heard. This might be a case of Nintendo favoring someone who's based in Japan and has experience with the Japanese entertainment industry. Hard to blame them for that.
... Or maybe the Alsace is strong in her or something :lol. Then again, her accent doesn't sound Alsacian to me. Or she's lived in Japan and spoken in Japanese and English for so long that she's actually lost a bit of her French. It can happen.