All I lament is, that I do not think that she ever knew how much I loved her.
In 1882, more than 50 years after her death, he confided in one of his closest friends, Maria Giberne, that he often could not mention Mary's name without tears coming into his eyes.
On the Blessed Cardinal Newman website, Professor Barb H. Wyman offers a reflection on a poem that Newman wrote about his sister Mary's death, noting that it took place just before Epiphany:
The Feast of Epiphany celebrates the happy arrival of the Magi into Bethlehem bringing gifts to the newborn Christ. This date for Blessed John Henry Newman, however, was filled with sadness, for Newman’s beloved sister, Mary, on the 5th of January 1828, died suddenly at age 19. In this moving poem, Epiphany-Eve: A Birthday Offering, Newman majestically weaves together these two contrasting events, the glad feast and his sister’s devastating death, for Newman loved Mary dearly; she was particularly sweet and cheerful, even when she knew her death was imminent. The pain of her death saddened Newman into his old age. The spiritual effects were great, however. It caused Newman to be keenly aware of the transitory nature of life on earth, and made him more attuned to the “invisible” world all around. It also strengthened his trust in God’s providence. These things would find their way into his poetry. This poem was written on the second anniversary of Mary’s death.
In the second stanza, Newman makes the connection clear between her death and this feast as Mary's soul was the family's gift to the Newborn King--their best:
Herald veil’d of glorious morrow.
Speechless we sat; and watch’d, to know
How it would be; but time moved slow,
Along that day of sacred woe.
Then came the Feast, and we were told
Bravely of our best to bring,
Myrrh, and frankincense, and gold,
As our tribute to our King.
Please read the rest there.