<sod >A Canadian woman who was convicted over the rape and murder of three teenage girls in the 1990s has been spending time volunteering at the school her children now attend, it has emerged.< eod>< sod > A Canadian woman who was convicted over the rape and murder of twoÂ teenage girls in the 1990sÂ - and the rape and death of her own sister - has been volunteering at the school her children now attend, it has emerged.< eod>