Our 18yr old cat was put down earlier this year. Dd (7) knew she was ill. I told her we were taking cat to the vet and that she might not come home. I explained very carefully that sometimes animals get so old and ill that their lives are painful, tiring and not very happy. When dd went to school in the morning I warned her teacher (a wonderful woman). Vet did recommend cat death and we had it done immediately. Picked dd up from school and told her immediately what had happened. DD burst into tears but got big hug from best friend. We talked about the cat quite a lot over the next few days, remembering nice things, funny things about her etc. DD had a few good cries with me and with dh. It wasn't anything like as bad as I thought it might be. dd still talks about cat (7m later) but in sensible way, not over-emotional or maudlin. Death is a hard thing to understand, but I think you should be truthful, give a chance to say goodbye, don't over-react to tears - they're natural and right. Let your dd cry, be sympathetic but not sentimental. Children can be distracted very easily and an exciting thing like a wedding soon after is unlikely to be marred too much for a child, as it could be for an adult.