Do you believe in fate?

The ancients had a saying: “One good turn deserves another”. Yet, my sister did not see it.
My house is in the city. My sister is a smart girl, a good student and good-looking. In school, my little sister was awarded the titles of excellent student for 12 years and held the position as the class monitor or the youth union secretary for 12 years. At home, she was a hardworking, honest and wise girl. My sister was the exemplary for our tenement as well as the exemplary for the high school class. She was much beloved by friends.
Right at the early year of high school, many boys of rich families flirted her, but with the thought of being from a poor family, my sister refused all of them ...although some boys pursued her for 4 or 5 years.
Then she became a teacher with an excellent degree ... My sister is always the excellent teacher at the provincial level ... .Then because of the so-called love, my sister from a city girl came to the countryside to get married to a man who studied at the education university with her and he later taught at the same school ... .It is normal that the countryside girl will come to the city to get married and hardly anyone from the city comes to the countryside to get married. It is just because that my brother-in-law looked honest and gentle although they are poor ...
After living together a few years, my brother-in-law revealed his paternalistic and authoritarian nature and autism in the relation with others ... .What my sister wants to do shall be permitted by him otherwise she would be showered blows on her ...
At first my sister thought that she suffered for her little child ... .But for many times, she could not stand and took her little daughter far away ... But he found her back and promised to change ... But “Who drinks, will drink again”
The couple separated for 5 or 6 years now ... My daughter from a smart and quick girl becomes a thin withered and prematurely senile woman with a blankly and melancholy face... She is insomniac interminably and sometimes, she stood on the bridge with the intention of jumping down ... Meanwhile her peers have become successful and happy with their families ...
I always think the life is very fair ... But why, for my sister, it is the injustice ... Is this the fate... .How can we do now, would you please give my sister some advice!