The landlord is not required to include a refrigerator in the unit (unlike a stove, which is required).  However, if she installs an optional appliance, she is required to keep it in working order, regardless of what the lease or tenancy at will might say.  See 105 CMR (Massachusetts Regulations) 410:351: 

410.351: Owner's Installation and Maintenance Responsibilities. The owner shall install or cause to be installed, in accordance with accepted plumbing, gasfitting and electrical wiring standards, and shall maintain free from leaks, obstructions or other defects, the following:

(A) all facilities and equipment which the owner is or may be required to provide including, but not limited to, all sinks, washbasins, bathtubs, showers, toilets, waterheating facilities, gas pipes, heating equipment, water pipes, owner installed stoves and ovens, catch basins, drains, vents and other similar supplied fixtures; the connections to water, sewer and gas lines; the subsurface sewage disposal system, if any; all electrical fixtures, outlets and wiring, smoke detectors and carbon monoxide alarms, and all heating and ventilating equipment and appurtenances thereto; and

(B) all owner-installed optional equipment, including but not limited to, refrigerators, dishwashers, clothes washing machines and dryers, garbage grinders, and submetering devices designed to measure the usage of electricity, gas or water.

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