Is the wife sinful if she abandons her husband because he refuses to build a bathroom on the floor of her residence, which causes her hardship and health damage, especially since she suffers from diabetes?

The husband is obligated to provide for his wife equitably, and this includes providing suitable housing commensurate with the wife's circumstances and the husband's financial ability, as Allah Almighty says: (Lodge them where you dwell, according to your means). This includes essential facilities such as a bathroom and a kitchen.

If descending to another floor for the bathroom causes the wife obvious hardship and the husband is able to build a bathroom on her living floor, then he is obligated to do so. If he refuses, it is permissible for the wife to leave the home to alleviate the harm from her, as harm permits a woman to leave the marital home. However, if the husband is unable to do so, the wife must be patient until he can afford it or until they move to another residence.