She doesn't have to do anything she's not into. And she can complain about gravure idol if it affected her in a negative way.
There's criticizing the industry and then there's criticizing the fans. All the fans ever did was appreciate her beauty and dutifully show up to hear her screech into a mic at 10 when she wasn't very good at anything musical because they liked her gravure (and as she's still not that great at anything musical I bet those dutiful fans are still a significant portion of her audience now).
It's also worth noting that by no means was/is Imouto overall some sort of objectively abusive workplace according to all available evidence as multiple idols, including many who were around at the same time as Rei, still work(ed) with them as adults (or at least older than U15), including Anjyu, Asami, both Yamanakas, both Nishinos, and Rei's own sister Aya, among others. She's the only one with a serious complaint even in her own family (and it seems quite likely to me that she's exaggerating it to bolster the rock-and-roll angst of her background story for her image's sake).
And if it's her parents that she has an issue with, then again what do the fans have to do with it? How were we supposed to have any insight into her home life from pictures of her frolicking around in bikinis? (And also again, has Aya complained?)
Gratitude for the people who made you even if the circumstances weren't perfect usually benefits both of you. Immature young people like Rei could stand to learn that. If her face wasn't angelic and her ass didn't look tight in a bikini, she'd have no fanbase at all, musical or otherwise. Maybe she'd prefer that to not be the reality of the situation, but it is.
Now to be fair I haven't seen the original book so maybe she didn't attack her gravure fans specifically in which case I retract much of the above. But the fact is that Rei has sailed along her entire life on her beauty and erotic appeal towards easier opportunities that uglier girls or girls with more clothes on wouldn't have had. Maybe that's a hard truth, but it's a hard life. If she really doesn't want it the way she got it, then she can give it all up, but I'm not seeing her rushing to do that. So if she obviously wants it (as she clearly does) more than she dislikes the circumstances behind it, then some gratitude at least for the people who weren't behind the scenes causing her whatever issues she had would be best.