A Piglet Called Truffle - Helen Peters

Hattie rescues a tiny little piglet from certain death. But Hattie's parents don't believe in farm animals being pets and insist that Truffle must be sold as soon as he's big enough. So Hattie begins a campaign to keep him. In the end, it takes two lost guinea pigs and one cold, frosty, nighttime adventure to save Truffle's bacon...