Character Analysis
Rosemary is Jack's mom and she's kind of a hot mess:
My mother had faith in me. She didn't have faith in discipline. Her father, Daddy, had given her plenty, and she had yet to see the profit from it. (7.6)
It's clearly a family thing, and if she got beaten, it means she knows exactly what it feels like. So she doesn't lay down the law on Jack. But neither does she protect him from the abusive men that she attracts like so many stray dogs. The best she can do is keep quiet about it:
My mother didn't tell me what went on between her and Roy, the threats and occasional brutality with which he held her in place. (2.22)
She had "a strange docility, almost paralysis, with men of the tyrant breed." (5.11) She's scared of them, but she's also drawn to them, which lets somebody else repeat the smacked-around cycle instead of her. Maybe she feels like abuse is inevitable, and want to make sure someone else does it. Maybe it makes her feel like a protecting nurturer if somebody else can be the target of her son's hate. Either way, it's not exactly grade-A mother behavior, especially since she clearly can't protect him.
Ch-ch-ch-changes
At the same time, she's really hopeful, and her flighty nature hides the unwavering belief that something great is just around the bend. Jack appreciates "her freedom, her delight in her freedom, her dream of transformation." (1.7) and goes along with it even when it's not for the best. Both of them live in bad circumstances. Both of them have parts of their lives that they really, really hate. So they use their dreams of transformation to stay hopeful and to keep moving towards the future. Don't like where you are in life? Just make like Annie and wait til tomorrow—you'll be somewhere totally different.
Gentle
Rosemary seems to be a very quiet soul, which means she gets pushed around a lot… like when "Marian thought my mother should get engaged too and tried to fix her up." (5.20) We never learn exactly why she decides to marry Dwight despite her better judgment, but it might just be to get Marian off her back. That makes her easy to sympathize with, since she's pushed around like Jack is. It also means that she's unable to stand up for him when it counts.
So Mom becomes a kind of fellow traveller with Jack. Someone to boost him up when he's feeling low, let him get away with more than she should, and even feel the kind of pain he's feeling. She's not a great mom, but she is a loving one. You can't say that about many people in this book.