Life saving operation for beloved family dog

Hi our beloved family dog needs an operation to remove a tumour on her stomach we cannot get credit for this and the PDSA will not treat her as we haven't had treatment for her in the last 2 years. Vets for pets have given us an estimate of £3000 for her total vet bills including the operation and tests. We have 5 children who dote on Tilly and don't have the heart to tell them she will die without this treatment. Please help us to save our dog