What should I do in this situation with my wife who left without my permission and returned, then attempted suicide? Should I divorce her? And does she have the right to the Mahr (dowry), the furniture, and the deferred Mahr?

You should sense the nature of women and their innate constitution, and try to please your wife and explain to her that the matter was just a joke, then apologize to her. Then, explain to her the seriousness of a wife leaving without her husband's permission, and remind her of the stern warning regarding suicide. If she comes to her senses, then keep her. But if she insists on her stance of disrespecting her husband's obedience and threatening suicide, then there is no blame upon you for divorcing her, and you should choose the lesser of two evils. The dowry becomes due to the woman upon consummation of the marriage. She is entitled to her entire dowry and all other rights of a divorced woman if you divorce her without any condition. You may refuse to divorce her until she waives some of her rights for you.