Act of Envy by Barbara A. Shepherd

Jolene Grayson is a young, ambitious prosecutor in the Harris County Attorney's Office in Brisco, Montana. In the emotional drama of her mother's death, she discovers her dad, whom she had known all her life, was not her biological father. Upon finding her real father, she is met unfavorably by his children, who fear losing their inheritance to her. In the midst of the chaos of family, she has been given a shaken baby case to prosecute and told by her boss that she needs to win it if she wants her career to continue with his office. But she is faced with the decision of healing her family versus prosecuting her case when she discovers the mother of the shaken baby is her half-sister.