Sundari or Sundari Nanda was the younger half-sister of Buddha and sister of Nanda. She was the child of King Suddhodana and Buddha's aunt Maha Pajapati Gotami. She, like other members of her family, became a Bhikkhuni (see also: Nanda (Buddhist nun)) and an Arahant, like her brother Nanda.
Soon after his birth, Prince Siddhartha's mother (Maha Maya Devi) passed away. He was adopted by her younger sister, King Suddhodana's other wife, Maha Prajapati. She was later to become history's first Buddhist nun.
When she was born, Princess Nanda was lovingly welcomed by her parents: Her father was King Suddhodana, the father of the Buddha; her mother was Mahaprajapati. Nanda's name means "joy, contentment, and pleasure." She was so named because her parents were especially joyous about the newborn's arrival.
Nanda was known in her childhood for being extremely beautiful, well-bred, and graceful. To distinguish her from other Sakyans -- the Buddha's extended family -- with the same name, like her brother, she came to be known as Rupa Nanda ("one of delightful form") and Sundari Nanda ("beautiful Nanda"). Over time, many members of her family, the Sakyans of Kapilavastu [likely located in the vicinity of Bamiyan, Afghanistan -- sakya literally meaning "grey earth" according to Wonderlane -- formerly the mountainous desert northwest of India, or less likely but as is traditionally held, southern Nepal) left the worldly life. They renounced it for the ascetic life, inspired by the enlightenment of Prince Siddhartha, who came to be called the "Sage of the Sakyas" (Shakyamuni).
Among them was her and the Buddha's brother, Nanda, and their cousins Ananda and Anurudha, who were two of the Buddha’s leading disciples. When their mother became the first nun, many other royal Shakyan ladies, including Siddhartha's former wife, Princess Yasodharā, became Buddhist monastics.
So Sundari Nanda also renounced the burdensome household life. But unlike many of the others, who sought the best guidance, she did not do it out of
confidence in the Buddha's enlightenment
confidence in the efficacy of the Dharma to bring one to enlightenment
confidence in the success of that Noble Sangha who followed the Path (the Buddha-Dharma) laid out for quickly reaching enlightenment.
She did it out of love for and attachment to her relatives and a feeling that she belonged with them.
It soon became obvious that Sundari Nanda was not focused on her life as an ascetic nun. Her thoughts were mainly centered on her beauty and popularity with the people, characteristics she enjoyed due to the ripening of meritorious actions performed in past lives. This welcome karmic inheritance became an impediment to Sundari Nanda. She neglected to reinforce it with new merit (profitable karma or weighty good actions).
She felt guilty that she was not living up to the lofty expectations of others. She was far from the goal so many members of the Shakyan royal family had left the home life for. And she felt certain the Buddha would censure her. So for a long time, she avoided him.
One day the Buddha requested all the nuns come to him individually to hear the teaching. Sundari Nanda disregarded the request. The Buddha asked for her to be called explicitly. She presented herself but her demeanor was abashed and anxious. The Buddha wisely appealed to her positive qualities, so she became willing to listen and delighted in his words.
When the Buddha knew the conversation had raised her spirits and made her joyful and ready to accept the Dharma, he began to teach her. Since Sundari Nanda was preoccupied with her physical beauty, he used his psychic powers to produce a vision of a stunningly beautiful woman, one more gorgeous than Sundari Nanda.
The woman then began to age rapidly and forcefully right in front of her. As a result, Sundari Nanda could see in explicit detail what humans otherwise only notice after decades or an entire lifespan: Youth recedes, health and beauty fade, decay and signs aging appear -- wrinkles, hair greying and loss, decline in faculties.
The vision deeply affected Sundari Nanda; she was shaken to the core. Having seen the image, the Buddha could explain the universal mark of radical impermanence [which is not about eventual aging, but moment-to-moment rising and falling of the Five Aggregates) to her in such a manner that she penetrated the truth entirely and thereby attained the first stage of enlightenment, certainty of future liberation, stream-entry.
As a meditation subject, the Buddha advised her to contemplate the impermanent and unpleasant aspects of the body -- to see it as it truly is and thereby be liberated by that truth. This is a systematic contemplation -- the first of the Four Foundations of Mindfulness -- not simply an epiphany (satori) based on a vision of the future loss of beauty. Sundari Nanda persevered for extended periods of practice "diligent and courageous day and night." She described it as recorded in the "Verses of Enlightened Nuns" (Therigatha 82-86):
Ill, impure, and offensive as well,
Nanda, see this jumbled mass [the body).
Toward the unlovely, develop mind
Well-composed to singleness.
As is this, so was that
As that, so will this likewise be.
Exhaling foulness, evil odors,
A thing delighted in by fools.
Diligently inspecting it, just as it is,
By day and night thus seeing it,
With my own wisdom having seen,
I turned away, dispassionate.
With diligence, carefully
I examined the body
And saw this as it really is --
Both within and without.
No longer lusting but quenched
Within this body then was I:
By diligence from fetters freed,
Peaceful was I and quite cool.
As Sundari Nanda had once been infatuated with her physical appearance, it was necessary for her to apply the meditation on bodily unattractiveness to counterbalance that powerful tendency and bias and find equanimity (impartiality).
Later the Buddha recognized his half-sister as being the foremost amongst female monastics who practiced meditative absorption (jhana) -- like the chief female disciple Uppalavanna and chief male disciple Mahamoggallana. This meant that she not only followed the analytical way of insight, but was expert in the foundational stages of serenity.
Enjoying this pure supersensual well-being, she no longer needed any sensual distractions. She enjoyed inner peace at will, in spite of having become a member of the Sangha out of attachment to her loved ones.