Question: How did Sien die?
About the article "Sien (Van Gogh series)", section "Abstract".

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Discography.2006: "Bloeisels".
Track listing "Verander Die Wêreld Deur By Jouself Te Begin" - 3:52 "Gedagte Vir Die Dag" - 3:09 "Sien Is Glo.. Jou Keuse - 3:44 "Die Beskermer - 4:05 "Die Avontuur Van 'n Hartbreek - 3:35 "Kan Ek Met Jou Dans - 3:24 "Bloeisels - 2:39 "Blanke Skaamte - 2:27 "Jou Seer Is Die Brug Na Iemand Anders Se Hart - 3:40 "Totsiens - 5:14  
My Sarie Marais is so ver van mij af<br>Ek hoop haar weer te sien<br>Sy het in die wijk van Mooirivier gewoon<br>Nog voor die oorlog het begin<br>Chorus: O bring my terug na die ou Transvaal<br> Daar waar my Sarie woon<br> Daar onder in die mielies by die groen doring boom<br> Daar woon my Sarie Marais  
At the end of January 1882, on his own account, van Gogh met a homeless, pregnant, prostitute named Clasina (Sien) Maria Hoornik who had been deserted by the father of the child she was carrying.
The exact date of this meeting is not known beyond van Gogh's dating of it in a letter to Theo written in May.
However another letter written mid-January mentions he was negotiating modelling with "a mother with a little child" and it does seem plausible this was Sien.
It has also been suggested that the woman he "found" following his humiliating rejection by his cousin Kee Vos, as described in a letter to Theo around 23 December the preceding year and immediately before his final estrangement from his father that Christmas Day, was in fact Sien, although there is no direct evidence for the surmise.
If so, he cannot nevertheless be the father of the child she was carrying because the dates do not fit.
Sien was born in 1850, the eldest of ten children of Pieter Hoornik, a porter in the poor district of the Geest, and his wife.
Pieter died in 1875.
To provide for the family Sien and her mother worked as seamstresses and cleaned homes.
Their earnings were supplemented by what Sien's brother, Pieter, could provide from the income of his chair-making business.
The family often relied upon public assistance.
For a time Sien and some of her siblings lived at a Catholic orphanage, relying on assistance from the public soup kitchen and church charities.
So meager were her earnings, she turned to prostitution for a better income.
At the age of 32, the unmarried Sien had given birth to four children, two of whom lived: Maria Wilhelmina born about 1877 and Willem born July, 1882.
Sien experienced poor health due to the post-operative effects of earlier surgeries, illness and venereal disease, which she seems to have passed to van Gogh who was hospitalized in June 1882 for gonorrhea.
Sien posed for van Gogh throughout the winter.
In exchange van Gogh provided Sien and her daughter a place to live and food to eat.
Sien was ill when he met her and he did what he could to nurse her back to health.
Van Gogh considered marrying Sien to take care of her and keep her off the streets.
He envisioned a life where Sien would be his helpmate, helping him further his artistic career.
Sien wanted to be married to him, too, even though he was poor.
His family, including his brother and supporter Theo, were against the relationship and his hope for continued support was doubtful.
In June 1882, van Gogh was hospitalized for gonorrhea.
Disobeying doctor's orders, he left the hospital July 1 to visit Sien in Leiden where she had just given birth to a baby boy.
Van Gogh moved to a larger studio next door with Sien and her two children.
Sien required an extended period of recovery from a difficult pregnancy and delivery.
The baby boy, though, seemed to bring a lot of happiness to van Gogh.
He explained that while he endeavored to go deeper as an artist, he was also looking to do so as a man. 
  "Als Ot en Sien", ("like Ot and Sien"): childishly simple.
"Uit de tijd van Ot en Sien", ("From the time of Ot and Sien"): from the good old days, from olden days.  
The works of Sien, a 32-year-old prostitute and seamstress, often depict her in traditional domestic feminine roles: a mother, seamstress, and domestic worker.
In the drawing "Sorrow" (F929, F929a) and a subsequent lithograph (F1655), Sien represents a woman's sorrow and frailty.
Some of the works are iconic, such as "Woman Seated" (F935, JH143) and "Mother with Child".
When van Gogh made drawings of Sien sewing, the compositions were simple as was her work.
If she had been in a higher station in life, a painting of her sewing would no doubt have shown her performing embroidery.
Rather than being an activity for enjoyment, Sien's sewing was one of drudgery.
Regarding "Woman Seated", it is curious that he posed Sien in a dress identical to one worn by Kee Vos Stricker, as can be verified by the photograph of Kee Vos and her son catalogued in the Dutch national archive "Geheugen van Nederland" and held in the collection of the Van Gogh Museum, Amsterdam (reproduced top left).
In a letter van Gogh mentioned how he considered Sien his helpmate or partner in the creation of the works which depicted her.
van Gogh would write Theo about his relationship with Sien, saying that it wasn't exactly love between them but rather a mutual understanding.
Vincent took Sien off the streets and provided for her and her children, and in return she posed for him.