Siobhan Fairbrother

Siobhan Fairbrother was one of the twin daughters of Barry Fairbrother. As she was in the same school year as the other teenagers in the novel, she was presumably about the same age.

Etymology
Siobhan (approximate English phonetic spelling "She-vaun") is a Gaelic name meaning "God is gracious". It is a cognate of the English name "Joan" or "Joanne", and of the Scottish name "Judith".