Final answer:
A cooperative owner has exclusive use of her unit by virtue of a proprietary lease, which is unique to cooperative housing arrangements and provides rights to occupy a specific unit.
Step-by-step explanation:
A cooperative owner has exclusive use of her unit by reason of a proprietary lease. Unlike traditional leases, a proprietary lease is associated with cooperative housing, where the ownership structure allows residents to own shares in the cooperative corporation which in turn owns the property. This ownership stake gives residents the right to occupy a specific unit and is accompanied by a proprietary lease that grants this exclusive use.
An easement refers to the right to use the property of another for a particular purpose, but it does not grant exclusive use of a housing unit to an owner. Therefore, easement is not the correct answer in this context. Similarly, a lease agreement may grant use of a property, but in the context of cooperative housing, the specific term is 'proprietary lease.' Joint tenancy is a form of property co-ownership that gives individuals equal shares and rights in a property, but it does not pertain to the exclusive use of a unit within a cooperative.