At first she feels deceived by Romeo. Her first words in reaction to the news of him killing Tybalt is
“O serpent heart, hid with a flow’ring face!/ Did ever dragon keep so fair a cave?/ Beautiful tyrant! fiend angelical!"
Then the Nurse joins in on blaming Romeo, and Juliet jumps to Romeo's defense. After all, that is her husband. She immediately feels ashamed for having called him those names and she scold the nurse for her negative comments about Romeo.
“Blister’d be thy tongue/ For such a wish! He was not born to shame. / Upon his brow shame is asham’d to sit"
So Juliet's first reaction was to feel betrayed by her husband. She felt grief for the loss of her cousin. However, after hearing another person say negative things about him, she felt guilt for badmouthing him, too. Her emotions are all over the place because she has to take in many different emotions all at once. She lost her cousin. Her secret husband is to blame, and then he will have to run from the law, which will add more complexity to the situation. This poor, young (child) girl has to go through many emotions in a short period of time.