Yeah, she's indeed not a normal ghost, that's for sure, especially when compared to other spirits shown so far. It's funny though because while I still think it could be plot related, her lack of voice (or text bubbles lol) is a nice artistic choice since, well, she's an idol and her voice should be one of her main selling points.
Let's see what the next chapters will bring to the table, it's a lovely series so far so I trust the author to deliver in one way or the other!