Please help me find this 90s/00s crime fiction about a murdered woman.

Hi,

Really hope someone can help with this as it's been bugging me for 2-3 years now. Basically it was a sort of crime fiction (although not really a thriller) about a woman who had been murdered on her way back from a parent's evening in a small village. The book was written from the perspective of her best friend who goes about her daily life and can't move on/ get over how such a thing could happen. The best friend has an affair with the murdered woman's husband and I can't remember who the killer turns out to be. The book is set in a remote seaside town and I believe was written by a British author.

Many thanks!