Bag, I am sorry your sis' friend had such an experience. You said her family bullied her...? Then in time he abused her? I have no idea and its already over. There are many question marks as to pin pointing how this triggered such a tragedy. All I know is: She was not prepared for this.
I have no idea she considered how her husband's family would treat her before their marriage. Maybe they did not understand each other better enough to take care of the issues that happened. Perhaps they do have some issues during their few year courtship before the marriage? I don't know and there are so many factors leading to all these.
Some women are weak in the heart? Some men too are weak in the heart.
Maybe its just two harmless materials that, when fused together, will form into a deadly concoction.
Maybe the husband wanted to rely on her for some form of support? BUT unable to do so or did it wrongly? We never know, its my conjecture. I am not even sure what made the husband's family so "hostile" towards her? We never know what is going on and its never good to dig up anyway.
Its really alot of work when going into a relationship with the opposite sex and then further on into marriage and living together for life. Perhaps its one of the reasons why many people do not want to settle down and simply just go for "short term" relationship?
