St land transfer

As per the query 
The facts that you stated it fall under the category of Section 99  which states that restriction on transfer of bhumidhar belonging to ST.
No bhumidhar belonging to a scheduled caste shall have the right to transfer, by way of sale, gift, mortgage or lease any land to a person not belonging to a scheduled caste, except with the previous permission of the Collector in writing .
So here the mandatory for your ST grandmother is to seek permission from the DM and if the DM gives permission, the land may be transfer from tribal to non tribal person.
In the case of Adivasie  sarvangin vikash Samiti vs State of Maharastra and others ,justice D.Y chandrachud  stated that “where there is a specific bar to transfer the property from tribal to non tribal person without seeking permission  of appropriate authority, builder, developer cheats the tribal, So it is mandatory for the tribal transferor to take a prior permission of the DM.