Staying in abusive relationship because "God forbid divorce"

Recently I realized some of the people I know are in abusive relationship. 
I mean abusive physically and emotionally. 
One of the victim I know is a mother with 3 kids, the husband will kick and hit her (once with a chair), in front of the kids. He stomped on her, too. And this had happened for maybe...15years?
She said she is a Catholic and will not divorce since God forbid divorce. She was adamant for this reason, even when the Clergyman at her Church became concerned and OFFERED to help her apply for annulment. Still, she declined.
Since then, I was more aware of the peoples who stays in similar relationship. They are not dependant financially to the abuser, but still choose to live together because of the sin of divorcing.
Now, I post this topic because I hope to understand why they stays in toxic relationship. For all I know, God loves us and wants us to be happy. If we tried our best, and the abuse continues, I believe it is time to pack up. 
Is the sin of divorcing an abusive partner so great? 
Does God really wants us to stay in abusive marriages? 
Please do give me some of your opinion. Thanks
Edit: thank you sooo much for your replies. 
I was wondering if I am mad or sinful for thinking divorce is alright (due to abuse). 
As for the above case, I tried to gave her courage, and she did realizes the impacts of it to the children, yet, she still chooses to stay. And stayed far away from me.
I have tried my best for her, and now I can only wishes her well.
As for the others, I can only be there for them. I can't pull someone out of the relationship, if they are not willing to leave it.