I reckon that she'll be true to her native land but then defect at the last minuit and save Noctis and Co.
Oh, and I'm pretty sure it's already been confirmed by Nomura that Stella is not the mysteriuos Dragoon.
Oh, and on the topic of Stella, why did they have to go and change her mature look for another generic "pretty" teen? Same with prompto - WHAT HAVE THEY DONE TO YOU!?
(Not for the feint of heart)