Which tragic news come to Helen in February 1896?

Although we have not heard of the gentleman in the memoir before this point, Helen Keller writes at end of chapter 12 of the death of Mr. Spaulding:

these bright days were darkened by the greatest sorrow that I have ever borne, except the death of my father. Mr. John P. Spaulding, of Boston, died in February, 1896.

Keller goes on to explain that he was a person who

made every one happy in a beautiful, unobtrusive way, [and] was most kind and tender to Miss Sullivan and me.

She states that Mr. Spaulding always took a great interest in the work she and Miss Sullivan were doing and that they all always felt safe with his protection of their interests at hand. Helen continues by saying that Spaulding's death has left a "vacancy" that has been unfilled.
Toward the end of the memoir, she includes a letter she wrote to Mr. Spaulding. It appeals for his help in a difficulty and gives some insight into how they worked together for charitable causes. She and Miss Sullivan were having a tea to raise money for a kindergarten for blind children. However, the house where they had planned to hold it could not fit more than fifty people, and they expected many more. Keller appeals to Mr. Spaulding for help in finding a bigger space. In response, his sister does open her own home for the event. The tea raises $2,000. According to the inflation calculator, that $2,000 would be worth more than $50,000 today.

In February 1896 Helen was brought the tragic news that John P. Spaulding of Boston had passed away. It's a measure of just how highly regarded Mr. Spaulding was by Helen that her sorrow at his passing was exceeded only by the death of her father, someone else she deeply loved, cherished, and admired. Mr. Spaulding had been a close friend of the family, a source of great comfort and support to Helen. An elderly bachelor, he was a wealthy man known as "The Sugar King" of Boston. He donated large sums of money from his sugar business to various philanthropic ventures and generously acted as a financial benefactor to Helen and her family. He was a warm, caring man, someone who had been immensely supportive and encouraging both to Helen and her close friend and assistant, Annie Sullivan. As Helen puts it herself, Mr. Spaulding's passing left a vacancy in their lives that would never be filled.