“She’s grown just like Mr. Simms and she should’ve stood up for me. I wouldn’t have done her that way.” Who said this? Who is the grown person this quote speaks of?

Cassie makes this remark about Big Ma.

'Cassie,' he said, in a quiet, thoughtful voice, 'don't go blaming Big Ma for what she done.'
'Why not!' I asked angrily. 'She made me apologize to that ole ugly Lillian Jean 'bout something wasn't even my fault. She took them ole Simmses' side without even hearing mine.'
'Well, maybe she couldn't help it, Cassie. Maybe she had to do it.'
'Had to do it!' I practically screamed, ‘She didn't have to do nothin' ! She's grown just like that Mr. Simms and she should've stood up for me. I wouldn't've done her that way.