Being nice and caring is overrated, anyway. The cold brutality is that what counts first and foremost is biological attraction; how well would your genes mesh with hers (as determined by getting a whiff of your body odour). If you have the "right" genes, a woman will find all kinds of excuses to like you even if you are a total asshole.
Women also generally think about how well you would be able to look after her and any children that may come out of the relationship. That's a biological program and not a character fault in women.
One of the things we have to learn in life is that we have the mate we need, not the mate we want. So, Dom, if your friend keeps ending up with men who you think are not good for her, there must be a reason. Like women with an alcoholic parent who end up with an alcoholic partner because that's a situation they are familiar with and know how to handle, even though they hate it.
And move on from her, you are wasting your time, and your life.