She is the only daughter of Jack Mooney. Siobhan takes care of her father and worries over him. She travels to Saint Marie with him on holiday, and he asks her whether she wants to make it a permanent home. She asks to think about it and eventually tells him she thinks they should stay. Siobhan's mother (Jack's wife) died around a month prior.
Although Siobhan's father has an Irish accent, Siobhan's accent is English.
At the beginning of series 7, Siobhan leaves her father to travel back to the UK to attend university, having decided not to defer for a further year. She is taking a place at St Catherine's University to study a BA in Philosophy.