Is it permissible for a woman to write a will stating that the apartment her husband put in her name should rightfully be entirely his, or to do something that guarantees his right, fearing that her brother—who is undutiful to his parents and ill-mannered towards her—might inherit from her, especially since the apartment is entirely the result of her husband's efforts?

A woman is not permitted to write a will bequeathing her apartment to her husband after her death, because it is a bequest to an heir, and a bequest to an heir is legally prohibited.

If the husband wrote the apartment in her name as a valid gift, meaning she received it during his lifetime, and he cleared his belongings from it, and she began to dispose of it as an owner, then the gift is complete.

However, if he wrote the apartment in her name so she would take it after his death, out of a desire to prevent his siblings from inheriting from him, then this writing is also a bequest to an heir, and it is legally prohibited.