The first thing you need to know is that U.S. libel law is much more favorable to defendants than the laws of many European countries, particularly Britain. That is to say that a suit that would likely lose in the U.S. might well prevail in Britain. And the rich and powerful might go "forum shopping" to get a favorable British judgment. Americans are protected by Rachel's law, which hinders a U.S. court from enforcing an British judgment (unless the American goes to Britain). Most European countries would not give you such protection, and in any event, it's probably easier to collect a British judgment in Europe than in the U.S.
The rest of what I have to say refers mainly to U.S. law. I am an American and not a lawyer. I am writing as a writer and prospective juror (trier of fact).
The first thing about U.S. libel law is that the burden of proof is on the plaintiff. In Britain, the burden of proof is on the defendant. That's why defendants tend to win in the U.S. and lose in Britain. As a juror, I would give you the benefit of the doubt. Many, perhaps most, would.
The second thing is that truth is an absolute defense against libel (although "publication of private facts," such as someone's social security number, is a separate offense). So dmm's advice about "sticking to the facts" is a good one. One way to do this is to juxtapose different outfits on a time line, coupled with her ratings on different dates, both of which are facts. What you want to avoid are speculations about motivations, etc. "Miley did X because of Y." Instead, you want to let readers draw there own conclusions. (Note that you could probably get into trouble in Britain for juxtaposing "inconvenient" facts about someone even if they are individually true.) In doing the above, you will want to consult a lawyer, or at least a language expert, such as an editor or English teacher.
It is a very important fact that Miley Cyprus is a public figure, because U.S. "case law" (precedent) makes it very hard for public figures to win libel suits. Basically, it is not enough for the public figure to show that a defendant's statements were false, but were made with either "malice" or a "reckless disregard" for the truth. As a juror, I would find that your consulting a lawyer, or language expert mitigates against a "reckless disregard" charge. Such a person would help make your statement "legally accurate," to use a phrase coined by an American President.