I always love when people who most likely aren't linguists or have ever studied linguistics in their life think their opinion matters on things like translation quality
The author's intent, not words, are what matter. In this case the author intended to write a trans girl, so the term was localised to trans girl. It's that simple.
If anyone wants to continue to complain about trans characters being included in things, however way they might be worded in the original, here's my advice to you: either put up or shut up. It's always the same people. It's always "hurr durr but that wasn't what the author meant in the raw!"
It's nearly always targeted at trans characters existing. So come on, if you hate trans people so much you want to insult or erase them in stories that feature them, do your own translations or stop complaining.