Although gun ownership is more common in Western MA Somerville has a very low gun ownership rate (2.04%). The Cambridge rate is even lower, at 1.01%. Alabama has among the highest gun ownership rates in the nation, with around half of all adults owning guns. I’m not surprised the roommates came into the apartment with different expectations as to gun ownership.
This is why I assume between the time the roommates confronted her about the guns and the time of the inspection by the COP she’d gotten herself a gun safe, as required for storage under Massachusetts law. She does not yet have a MA permit but submitting an application and scheduling her interview probably puts her in compliance.