It is hard to tell, people in abusive relationship do not like to tell.
Research prove, the main reason that cause a woman to be in a relationship, is due to unreleastic expectation cause by something professionals refer to as "Response Shaping Process", it is a form of method, of persuading a person to believe in a particular believe when they are yet to have the opportunity to develop an opinion of their own, it is extremely effective amount children. The reason is because when you have lesser understanding, it is easier to persuade you, because you do not have the require knowledge to contradict what you are been persuade to. Communist and Nazi also use these to brainwash children too. Girls in the west, are frequently been taught by their mother a problematic point of view about what true love and true happiness is and what is the necessity of life and because they were children,beliving in that, true love is romance, knight in shinning armor, Cinderella style fairtale romance and that having a man is necessity.
As a result, some woman who do not have a man, would settle for a substandard male, even an abusive one, believing having an abusive man, is better then having no man. Some will go out of their way to find romantic relationship, some of these relationship can be both romantic and abusive in the same time, but the girls choose to stay in this relatioship anyway. To keep a woman with him, the abusive man, will also frequently attack their self esteem, in regards to their physical appearance, low self esteem in their own physical appearance, make them fear not able to get another man, if they leave this relationship, a lot of these attacks are rather vage.
It is difficult to tell if a woman is in an abusive relationship, the first step to help them is get them to understand, it is alright not to have a man. That fairy tale are just stories, they are just fiction, not reality and they need to let go of their believe in regards to fairytale = happiness. Remind them that while in story such as Snow White,say the princess live happily ever after, they never give a justifiable reason why, if Snow white's prince is a funny guy who love her, then it might justfy happily ever after, but if he is a man who lock her in the dungent and whould chop her head off is she don't give him a mle heir, well if that is true happiness then we rather don't want it.