The term "feminist character" needs to be examined first. This could mean (1) a character who herself exposes feminist beliefs or (2) a character who, whether herself espousing feminist beliefs or not, was created by an author as part of an explicit intention to raise feminist issues in a literary work (3) a character who does not espouse feminist beliefs created by an author who did not intend a feminist viewpoint, but nonetheless used by feminist critics to illustrate feminist issues.
It is most likely that Nora falls under (3). Although Ibsen does have several strong feminist characters (Hedda Gabler is another), they do not really espouse general feminist beliefs, but rather are rebelling against their individual situations (which may include their positions as women, but that doesn't seem to be the focus). Nora herself seems rather childish, and her ideals are rather the opposite of feminist (she wants a strong wealthy man to take care of her). Ibsen himself did not espouse strong feminist beliefs.
One way in which Ibsen came to be read as feminist was that he was championed in England by G. B. Shaw, who wrote a book called Quintessence of Ibsenism, advocating a radical revision to the nature of English theatre. Shaw was a feminist in several ways, and thus Ibsen was often received in terms of Shaw's theories of women in anglophone culture.