That's where the trouble lies - there aren't many who are senior to her who aren't spoken for. The main one who should/could be top now is Tomu, who is lined up as Nibante for Cosmos. Everyone thought Yuuhi would have a couple of shows then head off, much like Takashiro Kei, but since she's staying, Tomu's Top stint looks like it has been put on hold, and since she's also backed up by Micchan as sanbante and an upcoming Kacha rapidly overtaking Tomochin as Sanbante, they really have too many people in line for Top Star. So possibly Tomu?