What is the best psychological intervention (CBT, Adlerian, etc.) for a grieving mother of a child and why?

Lucy is a 50-year-old woman living in regional NSW. Lucy has recently started coming to counseling after losing her 18-year-old son, Jacob, two months ago who died whilst holidaying with his friends in Bali. The cause of Jacob's death is still unknown and the Balinese police have informed Lucy that the case is still 'pending an investigation'. At the time of his death, Lucy and her estranged husband, Don, traveled to Bali and found Jacob's body in the hospital mortuary. Since returning home, a funeral has been held for Jacob and Don has returned to his home in Tasmania. Up until his death, Jacob lived with Lucy and they had a close relationship. Lucy has no other children.

During the time in Bali and her immediate return to Australia, Lucy was busy making the arrangements and providing information to the Balinese police. Lucy feels as if she was numb throughout the experience at the time. However, she has recently lost weight, is struggling to concentrate at work as an emergency veterinarian, and feels angry much of the time. Lucy feels guilty for helping Jacob pay for his trip as she did not think he was mature enough to travel to Bali at the time. Lucy feels as if her estranged husband, Don, has been able to "return to his life in Tasmania" with his new partner and child. Lucy is exhausted and constantly feels frustrated by the lack of information and miscommunication from the police in Bali. Jacob's friends have tried to make contact with Lucy, but she is too upset when they call and text and does not answer or respond to their messages.