I’m not trying to sound like an arse, but you’re confused because you have not tried to educate yourself on DV. I live in Australia so I’ll give you those stats if you don’t mind: 6.3 times - that’s the average amount of times it takes victims to actually leave a DV relationship. There are psychological and sociological papers, hundreds, as to the reasons why people go back (fear, money, brainwashing, self esteem etc etc). There are thousands of websites (mostly run by charities) that are dedicated to helping victims AND their friends on how to support them. This woman isn’t the first to return, she will not be the last.

The attrition rates for rape in the criminal justice system are bloody awful - but domestic violence isn’t loads better (around 20% or lower of abusers are convicted), now only 22% of all other accused crimes (murder, theft, fraud) charged are normally convicted - but it’s around 70% conviction rate of at least one charge in all other crimes. So attrition rate for rape - 96%, attrition rate for DV - 80%, attrition rate for all other crimes - 30%.

These are all rough numbers, depending on country to country.