Mary wants to indicate that her property will serve as a camp for foster children. What type of estate does Mary want?

Qualified fee simple.

Explanation:

Fee simple is described as the freehold ownership right to the owner of a land that allows him/her to control, use, or transfer the property according to his will. Fee simple has been categorized into 'fee simple absolute' and 'qualified fee simple or fee simple determinable'.

As per the given description, 'qualified fee simple' is characterized as the real estate type which an inept/defeasible fee (estate) is created with clear instructions about the condition posed by the grantor to grantee that if a specific event/condition occurs, the ownership would be reverted and subject to repeal. Mary requires such estate as she wants her property to be used for providing shelter to foster children and if the condition occurs in which the land is being misused or used for any other purpose, the ownership would be subject to revocation. Thus, 'qualified fee simple or fee simple determinable' is the answer.