Miss Walter or Miss Walters (depending on who's talking about her) is Hilly's mother. She's an ambiguous character. She seems at once insane, senile, victim, victimizer, and rebel. She definitely has a soft spot for Minny Jackson, who worked for her for years before Hilly relocates Miss Walter to a nursing home. She does not have a soft spot for her daughter, Hilly, and delights in Minny's pie-prank, rubbing it in her daughter's face whenever possible.
On the one hand, we like anybody who socks it to Hilly. But, we also wonder if Miss Walter treated Hilly this way when she was a child, before she became a monster. We suspect that Miss Walter had a hand in instilling in Hilly the belief that black people are inferior to white people. But, these matters are complicated and without more info on Miss Walter, we can't speculate too much.