My father passed away 10 days ago and has been buried with Muslims in USA. My mother wants to reserve a place beside my father's grave so she can be buried next to him when she dies. Is that allowed in Islam?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

If the questioner means that his mother wants to be buried beside the grave of his father, then it is permissible.

There is no harm in reserving a certain place where one may be buried after death. The evidence for this is the practice of the Prophet as reported in a Hadeeth, that when ‘Uthman Ibn Math’oon died, the Prophet ordered a man to bring him a stone, but he was unable to carry it. The Prophet got up and carried it and placed it at the head of the grave saying: “I am marking my brother's grave with it, and I shall bury beside it those of my family who will die.”

All the above rules are applicable only if the mother is Muslim, otherwise she should not be buried with Muslims.

Allah knows best.