Complex sentence: She later returns to help after receiving Monroe and Rosalee's phone call and kills Juliette with a crossbow in the Season Four finale "Cry Havoc" after Juliette was trying to kill Nick.
Split into simpler sentences: She later returns to help after receiving a phone call from Monroe and Rosalee's. She kills Juliette with a crossbow in the season 4 finale "Cry Havoc" because Juliette was trying to kill Nick.