Niamh Fairbrother

Niamh Fairbrother is one of the twin daughters of Barry Fairbrother. As she is in the same school year as Andrew, Fats, Krystal and so on, she is presumably about the same age. Andrew describes her as the "less pretty" of the twins, implying that the twins are fraternal rather than identical.

Etymology
Niamh (approximate English phonetic spelling "Neev-uh") is a Gaelic name meaning "bright" or "radiant". It is thus a cognate of "Roberta", and probably of other English names.