I feel sympathetic towards Celeste.
She has married into a family where her husband is unusually close to his siblings. They are all extrovert and effusive in sharing their emotions, whereas she is more self-contained.
Due to her husband's poor financial decisions, she faced a dramatic reduction in circumstances and was forced to move in with his grandmother, who doesn't like her. Bear in mind that she is working from home, and the (retired) grandmother is there ALL the time.
Her husband then embarked on a year-long affair, but she was unable to leave him as there was nowhere for her to go, and she needed to keep a roof over her daughters' heads. She kept quiet about his infidelity to protect her daughters' relationship with their dad.
She also had a scare over her daughter attempting to get illegal, dangerous and life-altering surgery.
To then find out that her husband had asked for the OW to be contacted as next of kin when he became unwell must have felt like the last straw. I don't think I would have been polite either.