Why does the dead son's mother have a violent face in "The Sculptor's Funeral"?

The sculptor's mother has a violent face when she cries over her son's casket, when she interacts with her husband, and when she scolds her maid.
When Steavens, who has ridden with the hearse, arrives at the Merrick house, a "naked weatherbeaten frame house," the same group of men that have been at the station are at the gate, which hangs on only one hinge. Carrying the casket across warped planks through the dilapidated gate is difficult for these men. As they struggle with it, they hear the front door yanked open and a large, bulky woman breaks through violently, calling out loudly to her dead son in a maudlin way as she falls over upon his coffin.
Steavens cannot believe this woman is his mentor's mother; she is coarse and loud and brutish. She has power, yet she possesses a kind of "brutal handsomeness, that is scarred and furrowed by violence." This violence is evinced when she acts, as well. When, for instance, her frail husband tries to console her,

She turned with a cry and sank upon his shoulder with such violence that he tottered a little. 

Later, the mother scolds the poor maid, who grieves personally about the sculptor. When the mother sees this maid, Steavens is shocked as the harsh woman unleashes her violence upon this servant for some minor action: 

...it was injured, emotional, dramatic abuse, unique and masterly in its excruciating cruelty, as violent and unrestrained as had been her grief of twenty minutes before.

From his experience in the Merrick home, the narrator understands why Harvey Merrick fled his hometown, and why the gentle man felt that he had no choice but to flee.