Maybe it Has Been Done Before (but not by you)

I just received an email from a friend in England. She's an amazingly witty and articulate writer, but seems to have a difficult time just getting down to it. Anyway, she told me that she'd had a wonderful idea for a story while she was doing the washing up, but thought the idea might have been used before. Then she thought she heard my voice telling her to get on with it anyway!
Yes, just about every idea has been used before. But you, dear writers, have your own way of telling a story that hasn't been done before. Do you know how many Cinderella stories there are? Hundreds I believe. They come from France, Germany, China, England, America, The African Continent, and many other places too numerous to list.
So yes, there are tons of stories about mischievous children (and please - it's pronounced MISS CHEE VUS'), even more stories about naughty dogs (I'm writing one now, even though a friend of mine wrote the BEST series of books about a naughty dog named Stanley. The writer is Linda Bailey. Be warned though, her books are so funny you'll laugh until you hurt). There are tons of books about a kid on a quest in an alternate universe. But guess what? Each one is told in a different voice, and each quest follows a different path.
So if you think of a story that might have been written before, remember that it hasn't been written by you. My friend in England - the one doing dishes instead of writing - is correct. She did hear my voice telling her to "Get on with it!"
p.s. Actually, it reminded me that maybe I should be doing some dishes!