Frankly speaking, our choice of spouse is similar to our choice of rebirth in our parents' home now, which is determined by personal fate and karma. Otherwise, why did your sister choose her present husband in the vast sea of people? Why does your sister dislike this person now? At the beginning, your sister could see the advantages of her current husband. Why can't she see it now? You must find out the reason yourself. We must cherish and tolerate this relationship.
My advice to your sister is never to get divorced. There are too few cases of remarriage after divorce and too few cases of unhappy families. Frankly speaking, it is more difficult to find a better one after divorce. You can ask the person who came before you that it is more difficult for a remarried spouse than it is now. Both husband and wife must change in order to maintain a good marriage. It is often said that men should be strong and women should be gentle. "rigidity" and "softness" are tolerance, thinking in the heart and flexibility in practice.
Husband and wife should help each other. Both sides should respect their parents/in-laws/in-laws, love their families and take care of each other. We should tolerate each other, look at each other's advantages, don't argue when things are not going well, and tell each other the truth privately when the time is right. Both sides can tolerate and deeply understand the facts. How did such a family come to this step of divorce? How can a person be unhappy?