Popcorn

A childless couple knows that fostering a teenage girl with learning difficulties may pose certain challenges.
Soony has a sunny personality, an affectionate nature and a tendency to swear like a trooper and behave unpredictably in public.
She seems to be settling in well to her new life. Soony's social worker and the staff at her former care home are reassured that the placement is working well and that all three members of the new family are becoming attached to one another.
However, June and Jim are becoming aware that there is a fourth member of the family - Soony's imaginary friend Popcorn.
But is Popcorn imaginary?
And if not, who is she?