It's possible there was a typo or communications breakdown somewhere with the localization, does the Japanese/French script refer to her as a Summoner or a mere Arcanist?

If the job description are consistent between languages that it would prove to em that she IS a bona fide summoner. And if she is such than its likely that the Monoceros was a constrct of hers or that she had summons made form different primals (like say...Belias? The precedent was set and Bozja obviously has Ivalician ties)