After recently watching the movie Titan AE, no one mentioned the species of most of the aliens. However, during the credits, the species are indeed pointed out. Notable, Stith is listed as Sogowan as seen here:
https://i.imgur.com/HfADkBb.png
I embarked on a journey to try and find anything other than fan works that provide proof of the name "mantrin" being used anywhere and despite this, I found nothing. The movie lists her as Sogowan. The toys say nothing, the wikis provide no proof mantrin even exists. The closest I found was an unofficial description of a book referring to her as a mantrin.
Regardless, the movie, as in the source of the media she is from, lists her as Sogowan. This isn't listing her as a nationality as the other characters are listed as "Human", not "earthling", so it's not pointing to a place of origin.