Story of previous birth of mainly found in folktales and Krishna stories prevalent in Braj region. Demon Putana had attempted to kill little Krishna
by breast feeding him poisoned milk. She was unsuccessful in her mission and
was killed by little Krishna . Since Putana was
annihilated by Krishna , she achieved moksha.
Legend has it that Demon Putana in her previous birth was
the daughter of King Bali and was known as Ratnamala.
King Bali was conducting a yajna and Bhagavan Vishnu
appeared there in the form of Vamana. On seeing the dwarf Vamana, Ratnamala
desired that she should have him as her child in next birth and she should be
able to breastfeed the infant like a mother.
Vamana realized what is going on in the mind of Ratnamala
and blessed her that her wish comes true.
But later when Vamana crushes Bali
with his foot and sends him to the netherworld, Ratnamala is upset and blurts
out that if she gets a son like Vamana she will kill him by mixing poison in
her milk.
During Krishna avatar, Ratnamala as Putana gets opportunity
to breastfeed little Krishna like a mother and
she also gets opportunity to mix poison in her milk.
She thus achieves moksha and merges with the supreme soul.