Maybe she was abused by him and couldn't take it anymore. Or he was cheating and she snapped.
There could be various motives. It could be financial problems, where the husband's actions were causing severe financial distress for the family. Another reason could be that the husband was involved in illegal activities that put the wife and their lives at risk. Or maybe there was a long history of emotional neglect and the wife just snapped.
Well, it could be that the murderer was after something specific that the old man had, like a valuable heirloom. Also, if the old man had some information that could incriminate the murderer or someone else, that would be a strong motive for killing him. His cataracts might have made the murderer think he was an easy target as well, someone who couldn't identify them clearly.
One possible motive could be guilt. She might have been carrying the burden of the affair for a long time and finally decided to come clean. Another reason could be that she wants to end the relationship but felt it was necessary to be honest first.
Another motive could be the build - up of years of emotional abuse. She might have felt so trapped and hopeless that killing him seemed like the only way to end her misery.
One possible motive could be severe mental illness. For example, if a woman is suffering from postpartum psychosis, she may experience hallucinations or delusions that lead her to harm her children. Another motive might be extreme desperation. If a woman is in an impossible situation, like being trapped in a very abusive relationship and seeing no way out for her children, she might make this tragic choice. However, these are just some of the possible reasons and each case is complex.
Maybe the husband was mentally unstable and had a sudden burst of violence. Or, there could be a deep-seated jealousy issue related to something the wife did.
One possible motive could be a sense of inadequacy. The wife might feel that she can't fulfill some specific desires of her husband sexually, so she arranges for a hooker. Another could be a strange form of self - sacrifice, where she puts her husband's needs above her own feelings of jealousy or propriety.
One possible motive could be financial gain. If the husband was in debt or had a large inheritance at stake, he might have considered getting rid of his partner. Another reason could be jealousy. Maybe he suspected his wife of being unfaithful without any real evidence and let that emotion drive him to have lethal intentions. It could also be related to a mental illness that was undiagnosed, causing him to have irrational and dangerous thoughts.
The main motive could be to regain control and stop the trauma. But it could lead to her being judged by society, or having to live with the guilt. Maybe it also prompts changes in the law regarding victims' actions.
Perhaps she has some sort of control issues. By hypnotizing her husband into this state, she might feel like she has more power in the relationship. It could also be a very strange form of role - playing for her, where she wants to experience a different kind of dynamic in the relationship.