Well think of her character as Rola. A modell making a CD release "just in the sake of promotion and trying something new out". It's not like the character is having any lives in the manga. In fact, the only singing she do in the manga takes up like only one page in the whole manga, if even that much? The characters main field is modelling. My guess is that the only singing we will get in the movie is in a scene that takes max one minute.
