Continuity mistake: In the scene where Shirley and her daughter Milandra argue about Shirley going on holiday, Milandra gets out of bed and dresses quickly, her shirt is tucked into her jeans. She walks out and the camera angle changes to a view of her front, her shirt is now loose outside her jeans.
Continuity mistake: When Shirley is with her son in the squat in Kirby he sees a couple of kids robbing a car. When the car drives away you can clearly see that the kid driving is replaced by an adult stuntdriver.
Answer: Shirley stays. You can see that she has found herself and has fallen in love with herself and the life she created. After a life changing moment like that, she realises she can never go back again. She simply doesn't want to. At the end as she watches her husband walk toward her, you see that she observes him from a different perspective. She feels compassion, and she feels sorry for him even mentioning she hopes he stays a while to feel the sun on his face. You can sense the compassion she has for him in a more detached way and in that moment, you know without a doubt that she stays.