Character Analysis
It's almost like we're dealing with two different characters here. We have pre-Noah's departure Mama and post-Noah's departure Mama. The first Mama has it going on—she cares for her children well despite the fact that her husband has abandoned the family, and she generally doesn't take smack from anybody. She's the first to offer a room to Delphine and Calinda, and when the town busybodies give her a hard time, she gives them the what's what.
After Noah's departure, however, it's a different story entirely. As Tilly says:
I was crying like a lost child now. This wasn't the Mama I'd known. Who was this heartless stranger?
[…]
She whipped around quick, her hair flying, like she heard Noah's footfall on the porch. And I saw I'd lost her. She'd been whittled to madness by her fear. (9.29, 32)
Mama simply loses her mind with grief, treating Tilly with outright cruelty and finally drowning herself before checking to see whose body is in that coffin coming up the river.