I am not sure what the argument was...but for someone to leave because of an argument seems a little rash to me. There must be something else going on.
Does she have any mental disorders or a history of them? Is this the first time she said she didn't like your neighborhood or the people in it? Is her brother influencing her in some weird way? Has she always been close to her brother? Why would her brother let her stay there with 5 children in one bedroom? There are so many questions that I have...but I am sure you do too. I wish you the best. I am not sure if she is using you because I do not know her personally. I will say, people can say they love someone and not mean it at all. Some people are great manipulators. It is scary to think that you really do not know someone. I would tell her she either needs to put in a effort and come back and see a counselor with or without you, or you have to be done with her because this is unfair to you. At the end of the day, you are the one suffering. Does she care that you are distraught over this? If she did, she would not put you through this pain. Best of luck.