Hm, so it wasn't imagination on my part when I thought she looked rather ...subdued. I wonder, did they film the album announcement before or after Manakan's reception? Because I noticed it there as well. ^ This is my favourite theory too. I really can't imagine her not getting along with Manakan because a) who doesn't like Manakan?? and b ) Yanamin doesn't seem like someone who dislikes someone and isn't capable of being more 'neutral' about it in a public space.
I think Yanamin is really intimidated by her senpai and Ruru might be her gen mate but she's highly skilled as well. Manakan is such a natural at being idol ... I think she's just worried at losing the little spotlight she gained through her Sexy=Sexy center and photobook...