Dani is the 9th member because at first she wanted to practice more to make sure she's well prepared before performing together with T-ara. In previous news, she stated “In order to make sure I dont hurt T-ara's popularity or image, I'm practicing more before I join my Unnies“ but then she change her mind and said that she wants to perform with T-ara as soon as possible. And I think they put her in the MV to prepare the fans for her debut cause like now some QUEENS already hate her. She didn't do anything, she didn't choose to join T-ara, the CEO did. And Dani isn't all of over T-ara's next single, she's just in the MV. As you can see they released a Concept photo of Areum and Dani's info was released first because of the rumours that were wondering before they (CCM) got the chance to introduce Areum.