You are thinking it as if Ryann was a normal person. But she's not, she's a narcissistic attention whore, and this translates into her being a "mother".
Normal parents wouldn't abandon one of their kids to one of their exes, but narcissist parents? Their kids are nothing but props, and when they decide to not be props anymore (just like how Rilee asked to not be features on her socials anymore), they are to be left behind, if not discarded completely.
Look at Onision: he had a kid with his child bride to satisfy his impregnation fetish, and then completely refused to interact with the kid. His wife got pregnant a second time after they kicked out their "girlfriend" Billie, hoping that satisfying his fetish would restore their relationship, and as an answer Onision got back with Billie and almost ran away with her after signing both kids to his wife.
I knew a woman who sent her kid to live with his father in Argentina after not seeing him for almost fifteen years, because her new boyfriend didn't want kids and he didn't want to raise hers either.
PL, but my own mother sent me to live with other people while she was in the honeymoon phase with her new man because she thought I would spoil it.
Narcissists are awful parents, always, because they only think of themselves and that everything they do is right, but usually their kids realize it and go to therapy and learn that they were treated badly because there's something wrong with them, but because there's something wrong with the parents.