Hsu wanted to "depart quietly and peacefully" and left instructions not to make any announcement of her death in the news media, or perform any ceremonies that would "cause disturbance and inconvenience to others", said the notice.
The notice was signed by her co-worker Sharana Rao.
"She has further instructed that no claim be made of her ash by whosoever," it added.
Hsu, a trained nurse, devoted her entire life to helping the less fortunate.
Born in a tiny village in the Guangdong province of China, Hsu traveled to various countries, such as Hong Kong and Paraguay, to help others, before settling down in Singapore.
Here, she served first as an unsalaried matron at Kwong Wai Shiu Hospital for about three years before opening an old folks home, called the "Home for the Aged Sick".
After retirement, she turned her attention to her welfare service, Heart to Heart, where she reached out to needy elderly folks and families.
Yahoo! Singapore last featured Hsu in our Inspiring People column for her lifelong work with the less fortunate. Read more about her life story here.