I both hope that is and isn't the case.
I hope it is, because it would be nice if Ruriko wasn't just a bad mom and person who cared more about cultivating talent in her daughter than her family at large.
I hope it isn't, because it takes the wind out of Yuu's sails in trying to prove she's as capable as her sister, and worthy of her mother's recognition.
if Ruriko turns around apologizing at the outset for abandoning her, that's great--but Yuu might lose some of her motivation, turning to questioning why it had to happen at all, rather than focusing her energy into songwriting with Haru.
I could see a "both options" path, but Yuu's own journey started because of the tension with her mother. So that tension should be real, for Yuu's sake, to propel her to achieve her goals.
Why would that be a better story? Yuu's goals involve becoming a musician and songwriter that earns her mother's respect.
Outting Ruriko as a bad mom in the public eye doesn't achieve that, and only makes her look like a victim.
And that runs counter to Haru's own story of standing on her own and rising above her passive and timid self to become someone strong. Since the two of them are connected, something affecting/labelling Yuu would do the same to Haru, undercutting them both in a narrative sense.