Yeah she is definatly a Samurai. Unless she is one of those "naruto" styled ninja that look like samurai. Though thankfully that does not seem to be the case.
well historically ninja did where armor. Also historically, and more importantly, women were not allowed to carry swords. Wives of samurai were allowed to use a Naginata in defense of the home but never a sword. Therefore, must be ninja. Unless of course it's simply fantasy which, it likely is.