Who is Lady Helen Clyde from For the Sake of Elena and what is their importance?

Lady Helen Clyde is Inspector Lynley's love interest. She once refused to marry Lynley, and this put a strain on their relationship. Helen believes that in marrying Lynley, she would be giving up her inner self..... soemthing she is unwilling to do. What she fears most, however, is becoming like her sister..... saddled with children without a fulfilling career, and catering to her husband's every whim. Eventually, Helen and Lynley resume their relationship.