Ndileka Mandela, 52, has been told she should instead help revive the party.
She had earlier stated she no longer believed the ANC represented the values of her illustrious relative.
Ms Mandela said the party was neglecting to care for the poor.
"I will not be voting for something that does not resonate with me anymore, and does not resonate for what granddad and his comrades fought for," she told News 24 South Africa..