That's actually a wonderful bit of information, because I also felt "Hernandez" sounded way too Spanish. For reference, this is her name in the RAWS:
https://files.catbox.moe/158ntc.jpg
ミア・エルナンデス = Mia Erunandesu
Technically, I'd claim the katakana of "Fernandes" would be フェルナンデス, but I definitely like the look and sound of "Fernandes" more and, technically,
エルナンデス is just as much "F" as it is "H."
Depending on how her name gets written in the next chapter, I think a change to "Fernandes" is actually a good suggestion. Thanks, Mr. Brazilian~
EDIT: Oh, with more research, it really should have been spelled with the "s." She's clearly a nod to the judoka Daniel Hernandes.
https://en.wikipedia.org/wiki/Daniel_Hernandes
Thank you, once again, for commenting about the last name feeling "too Spanish;" that helped verify my fears that
something just wasn't right about the cute new trainer's surname. That will be changed!