In Act 3, Scene 2, Juliet is in a state of shock when she first learns that Romeo has killed her cousin Tybalt. Her first reaction is to feel that she had been deceived by Romeo and that she can no longer trust him. We especially see her newly developed distrust of Romeo in her string of oxymora:
O serpent heart, hid with a flow'ring face!
Did ever dragon keep so fair a cave?
Beautiful tyrant! fiend angelical!
Just opposite to what thou justly seem'st--. (III.ii.76-81)
These oxymora show us that Juliet judged Romeo's character by his handsome face, and now that he has killed Tybalt, it seems to her that his handsome face is hiding an evil heart and that he is the exact opposite of what he seemed to be when she first met him.
However, when Nurse next declares, "There's no trust, / No faith, no honesty in men," Juliet has an awakening (89-90). She becomes angry to hear her nurse speak badly of Romeo and realizes that she is most likely misjudging him and the situation. Juliet's next response is to exclaim, "[Romeo] was not born to shame" (96). Furthermore, through to line 106, she reasons that, as his wife, she should not speak badly of her husband. She reasons that, as his wife, it is her responsibility to continue to trust and honor him. She further reasons that Romeo is probably not ultimately to blame for Tybalt's death, that Romeo probably killed Tybalt out of self-defense, as we see in her lines, "But wherefore, villain, didst thou kill my cousin? / That villain cousin would have kill'd my husband" (105-106).
Hence, in this scene after learning of Tybalt's death, Juliet's attitude changes from feeling complete distrust and hatred for Romeo to realizing that she must continue to respect him as his wife and that he was not ultimately to blame.