My grandfather plans to give me one of his plots of land that I farm. He wants to include a right of return for my sister so that the land does not revert to my wife on my death.

The notary refuses to include this in the deed of gift. Why?

In accordance with article 951 of the Civil Code, "the donor may mention the right of return of the objects donated either in the case of the death of the donee alone, or in the event of the death of the donee and his descendants"
In this way, the property transferred to the donee returns to the donor's patrimony, and to that patrimony only. Paragraph 2 of the same article stipulates that the right of return can only be stipulated in favour of the donor (art. 951 al. 2 C. civ.), to the exclusion of any other person.