Clara Oswin Oswald is very clearly The Rani. Not only is she a science genius girl with a strong love of Souffles, but she is not 'Clara Oswald.' because Clara Oswald never existed.
Science Genius GirlEdit
In all of her appearances so far, 'Clara' has shown a preternatural understanding of the scientific workings of advanced technology. The only other times we witness a novice display such an immediate understanding of Time Lord technology is with Professor Doctor River Song, another time lord.
'Clara' may have jumped into the Time Stream of the Doctor's and survived. This is really hard to do. So far, 'Clara', or what ever her name is, has revealed to a cyberman that Clara is not her name, and that there was no Clara Oswald. Either 'Clara' was lying, or she really is someone else. Most likely a time lord, either the master or Rani.