Did she mean it as an arrogant jab at her enemies, as some writers have asserted? Was she expressing her joy in the most triumphant moment of her life? Or could it possibly have had another meaning that's somewhat lost on modern people?
The concept of personal happiness has changed dramatically over the centuries. We define "happiness" as an emotional state - the pleasurable feeling we have when we're with the person we love, or living in a time when things are going well with our jobs and relationships, a state of self-actualization and fulfillment. Today, we expect to be happy in life.We think something is amiss with our life if we're not happy and seek to repair it.
In Anne's time, people did not expect to have a "happy" life, as we would think of it. The world was seen as the "Vale of Tears," in which one could expect grief, strife, and suffering as one resisted the temptations to sin and tried to survive the onslaughts of the devil. Life was about duty and obedience to one's family and the Church. Happiness - as we define it - would come in Heaven for those who lived a virtuous life here on earth. Only the foolish and sinful sought a life of pleasure and personal indulgence.
According to Aquinas, real happiness on this earth was impossible to achieve because the world itself was a flawed, sinful place:
It is impossible for any created good to constitute man’s happiness. For happiness is that perfect good which entirely satisfies one’s desire; otherwise it would not be the ultimate end, if something yet remained to be desired. ... Hence it is evident that nothing can satisfy man’s will, except what is universally good. This is to be found, not in any creature, but in God alone, because every creature has only participated goodness. ... Therefore, God alone constitutes man’s happiness.”
--Summa Theologica Part 2. Q.1. Article 8
This is quite close to the earlier views of Aristotle that "Happiness is a life lived according to virtue.”
To the Tudors, "happiness" meant good fortune. Indeed, our word "happy" comes from the old Norse word, "hap" meaning luck. We retain some of that original meaning in the words "happenstance" and in phrasing like, "would happen to occur ..."
In Christian teachings of the day, good fortune was bestowed by God on worthy persons. By saying she was the "Moost Happi" Anne was saying she was "the most blessed," raised to this position by God. The meaning of the motto on the medal was actually more humble than it appears today.
The portrait medal itself was created for a specific reason, intended to be issued once the king's long-desired heir was born. The prince never came, and so the medal was never issued. We only have the badly-damaged prototype. Anne was not the "Moost Happi" after all.
Was Anne happy as we would think of it? Perhaps. We cannot know for certain of her personal feelings on the events of her life. Like most royals of the age, every moment of Anne's life was watched, and so she had to guard her words and actions, knowing they could be used against her by her enemies. (And, indeed, they eventually were.) Little record of her personal feelings survive, except for the times she lost her temper, and so Anne is sometimes interpreted as being a termagant.
Anne's family life might have caused her sorrow. Except for her brother George, she doesn't appear to have had a close relationship with her family. She had to send her sister, Mary, from the court when she married without the family's permission. We know that Anne sent Mary gifts after her disgrace, so there may have been fondness between the sisters.
It's said by some that Anne and her mother were close, but there's no real documentary evidence for it, like there is with Anne's brother. Anne's relationships with her aunts appear to have been indifferent or acrimonious. (Lady Shelton and Lady Boleyn were chosen to serve Anne in the Tower after her arrest, and Anne complained she had been surrounded by those she "never loved.") Despite whatever her personal feelings may have been, Anne did her duty in trying to advance her family during her relationship with the king.
When Anne had Henry's favor, she had the most potential for personal happiness. She lived in the most comfortable conditions for the time. Her clothing was of the finest materials, and her food was the best procurable. Her rooms always had a fire and charcoal braziers to heat them in the winter, and in the summer, she could move out of the stifling, reeking city for the cooler countryside. She had the most skilled medical care available. Henry indulged her every whim, and she was surrounded by her friends. She had pets and fools to entertain her.
Was it lonely at the top? We cannot know. Anne likely had a great deal of fun at the peak of her popularity, dancing and feasting at the court. But she was also under a great deal of pressure to always "perform," to be charming, witty, and graceful. Was that stressful for Anne?
Anne was expected to produce an heir, fast. When the baby she was carrying at her coronation proved to be a girl, Henry began to lose his faith that their union had been charmed and especially blessed by God.
Any personal happiness she had in her marriage was likely short-lived.