In Defense of Polly
She lost the love of her life Jason. She probably hated her parents due to them trying to keep them apart. Her parents send her away to the Sisters of Quiet Mercy, which would make anyone hate their parents for doing that. And in later seasons, it’s been revealed just how traumatizing the Sisters are. She never fit back into her old life in Riverdale. She then found the Farm.
There’s this one part where Polly returns after she’s given birth in season 2—I think this was actually an attempt to escape the Farm in a way. The Farm tried to cut her off from her family. Polly probably didn’t have enough strength to leave on her own, and she needed support from her family to completely break off. And she didn’t get it. And since the Farm is a cult, they wouldn’t take leaving very lightly. They’d find a way to bring her back, and if the Farm knew she was thinking about leaving, she’d be punished. She actually did leave for a while, to find herself out West. (Unless she lied.) She returned to the Farm, possible against her will. We don’t know what happened because she tried to leave, but it’s a cult, and cults don’t like it when people leave.