Bel-Imperia is the main female character of the story, and she has the misfortune to fall in love with both Andrea and Horatio shortly before they die. She also has the misfortune to have an evil brother in Lorenzo and to be the object of Balthazar's affection, when Balthazar is the very man who murdered her beloved Andrea and then went on to murder her beloved Horatio. She is then forced by both her father, the Duke of Castile, and her uncle, the King of Spain—the two most powerful men in the country—to wed this very same Balthazar.
Bel-Imperia does not, however, appear as a victim in all of this misfortune, which is a testament to the strength with which Kyd has portrayed her. He does this by giving her opportunity to display her rhetorical ability in stichomythia (line-by-line exchanges) between her, Balthazar, and Lorenzo. She also has several soliloquies, during which we have access to a mind, an interiority, with very strong opinions, desires, and motivations. We also have evidence that she has the necessary strength of will to act on her desires and motivations; the clearest example of this may be her participation in Hieronimo's revenge playlet, Soliman and Perseda.
Further, we can object that Bel-Imperia may be too calculating, too cold, and that her thoughts focus too much on revenge. Bel-Imperia, indeed, bears a vindictiveness for the wrongs done to her. Her love for Horatio seems partly motivated by a desire to revenge herself on Balthazar (which, of course, disastrously backfires in Horatio's murder). And she spurs Hieronimo on to revenge when he seems to be lazy in pursuing it. But this makes her murder at the end of the play acceptable—more acceptable, perhaps, than Hieronimo's actions. And as the litany of misfortunes above indicates, if she is angry, then she has very good reason to be.