Although Olive might think Shirley had acted to save Zac, in a very real sense, it was to save Shirley.
Shirley was not built to be the mother of an infant, and didn’t want to be. If she was a smidgen less responsible, she would run away and never return.
How did she come to this?
She recalled meeting Glen. He was handsome, fun, exploding with personality. She was in love with him in minutes.
She learned he was in the military, although he didn’t look it. He revealed he was Special Ops and on call for various clandestine operations.
In a way she thought it romantic, in another she was afraid.
Having lived with him for nearly two years, and he being deployed for nearly half of it, she was in a strange place of married/ unmarried.