There’s an ominous silence surrounding the tragic death of Pauline Silberstein whom Freud treated for a “nervous” disease. Sadly, Freud’s (mis)treatment of Pauline, aged 19, resulted in her violent death on May 14, 1891. Oddly, Freud never mentioned Pauline in his writings or letters. Significantly, Freud’s letters to Fliess, from the period between May 2, 1891 and August 17, 1891 (1), thus around Pauline's death, are missing.
Pauline was the wife of Eduard, Freud's youthful friend. How she died is shrouded in a veil of mystery, but there are some clues.
As Silberstein's granddaughter (from his second marriage) recounted, Pauline, became mentally ill and came to Vienna from Roumania to see Freud. She threw herself from a window in Freud's apartment building. This tragedy was corroborated by Anna Freud ... a few months before her death. (2) The family knew that Pauline was unsuccessfully treated by Dr Freud. (3)
According to the newspaper article in Neues Wiener Tagblat, on May 14, 1891, at 4.30 p.m., Pauline arrived at Freud’s location. While the maid waited outside, Pauline proceeded to Freud’s office.  She was never again to be seen alive. (3)
On only one occasion, Freud ever mentioned Pauline. Writing to the Jewish organisation, in Silberstein’s hometown, on April 22, 1928, when Eduard had died, in the letter, Freud, for the first time ever, revealed that he, once had occasion to attend to his first wife. (5) Freud’s attendance cost Pauline her life.
(1) Freud, Sigmund, The Complete Letters of Sigmund Freud to Wilhelm Fliess, 1887-1904, 1985.
(2) Freud, S. & Silberstein, E., The Letters of Sigmund Freud to Eduard Silberstein, 1871-1881, (1990, p. 192).
(3) Hamilton, James W. H., Freud and The Suicide of Pauline Silberstein, Psychoanalytic Review, 2002, p. 890.
(4) Freud, (1990, p. 186).

There are many unanswered questions about the mysterious circumstances of Pauline's death.
In their youth, Freud and Eduard were homosexual lovers. Strangely, Pauline's husband sent her to be mis(treated) by Freud in a faraway country, rather than letting her be treated at home.
But, did she really throw herself out of Freud's window? Or maybe she was thrown out by Freud? What speaks for the latter is the fact that she came to be healed, not killed. Also, the fact that she brought her maid with her to Freud;s house, and told her to wait for her return, indicates that she had no intention of killing herself.
Besides, why come all the way from Roumania to commit suicide? And why chose Freud's house when there were much higher location better suited for the purpose.
Was there some kind of sinister motive behind Eduard sending Pauline to Freud?  And what is most disturbing is the fact that any trace of Pauline, and her fate, had been expunged from Freud's published correspondence with Silberstein and Fliess , which hints at an ominous secret behind Pauline's death.
Did Freud try to "seduce" (rape) Pauline, which, at the time, was part of his cure? Did she resist Freud, and, in anger - Freud was a violent man - he pushed her out the window to her death? Or was Freud only fulfilling Eduard's wishes?

In his letter to Silberstein, of March 13, 1875, Freud, aged 17, tried to dissuade his boyfriend, Eduard, from getting involved with females. It's, an evil omen, he wrote, that you accept kisses so easily and ... that you take kisses so lightly.(1)  A couple of years later, in the letter of September 9, 1875, aged 19, Freud confessed his love to him stating, we shall never be rid of each other ... the one loves the very person of the other. (2)
Freud's interest in Eduard's love life continued.  Thus, in the letter of February 7, 1884 to his fiancé, Martha, Freud informed her that he, advised him [Silberstein]... against marrying a stupid rich girl. Annoyed, Freud explained that, he [Silberstein] is prepared to marry the girl. (3) Eduard followed Freud's advice. (The girl wasn't Pauline who, born on July 22, 1871, would have been only 13 at the time.)
In his book, The Making of an Illusion, 2017, Crews asked a pertinent question about Pauline's death. Did Freud still feel that Eduard Silberstein belonged to him ...? If so, and in view of his overbearing way with patients in general, it would have been in character for him to allow jealousy and malice to override his obligation to the fragile Pauline. (4) 
Could Freud have killed Pauline because she had replaced him in Eduard's affections? Or, would he have killed her, because Eduard wanted to get rid of a "mentally ill" wife?

Looking for a smoking gun

Notably, Crews is not satisfied with circumstantial evidence, writing that, Unless a smoking-gun document comes to light, we will never learn why the bride of Freud’s bosom friend hurled herself over the balcony.
As recounted earlier, it was claimed that Pauline threw herself from a window and not over the balcony.  One cannot but wonder where Crew's information comes from.  
And hoping for a smoking gun 150 years after Pauline's death is blatantly naive. Freud - assuming he killed her - wasn't stupid enough to leave behind this kind of evidence.  As Freud pointed out in his writings, hoping for evidential proof of murder was to underestimate the killer's (Freud's) intelligence and to overestimate one's own.
On the other hand, there's enough circumstantial evidence that Pauline was pushed to her death by the murderous doctor Freud. Had the police known all the facts of the case, Freud, without a shred of doubt, would have been charged, convicted, and sentenced to spend the rest of his life in prison.