My sister went through hell when she married her now-ex husband. She was not Catholic but in order to marry, had to have her previous marriage annulled. Her abusive ex then threatened to kill her since he now knew where she lived. Not sure this would have helped in that case. I was livid.
But, when her very devout husband left her for another woman, he did not bother to get an annulment. He and his new wife take communion and no one seems to care.
My empathies with your sister; I can totally relate to her situation. Insofar as her ex-husband and his new wife. they are either ignorant of church teaching or have chosen to ignore it. If they never apprised the parish priest of the previous marriage that was never annulled, how would the priest know?
Well I can think of one supreme person that cares, and His is the only opinion that really matters.
You and your sister were misinformed by someone. If your sister is not a Catholic, she certainly would not be required to seek annulment in order to remarry. That is just nonsense.
Sounds like there were some things similar to your sister and my brother’s first marriages. The last thing he wanted to do was to ever see his abusive wife who had homicidal tendencies towards him again. He stayed married to her for seven miserable years. When the danger to him escalated to near death situations, I started helping him hide from her. If he ever does go for an annulment, I hope they send a questionnaire to me.