The narrator's mama—much like the narrator's husband and daughter—has been reduced through memory to such an extent that she's more of a figurehead than a character. But hey: the narrator's #1 concern during this novel is trying to preserve her own identity, not the identities of the people she's lost.
We only meet the narrator's mother in flashbacks and we never learn her real name. We know the narrator's mom was a hardcore feminist and protester, someone who stood up for women's rights and participated in rabble-rousing events like the burning of porn. Some people might say that she wasn't always an appropriate mother: she brought the narrator to the porn burnings and let her watch Holocaust-related television programs at a crazy-young age.
She had her daughter late in life and raised her as a single mom. After her daughter was grown and she became a grandmother, she seemed to remain an independent person. The narrator's mother had the kind of dangerous individuality that was first to be snuffed out in Gilead.
Significantly, both the narrator and Moira see the narrator's mother appear in documentaries at the Center. In the one the narrator sees, her mother is a fresh and youthful protester at a "Take Back the Night" rally. In the one Moira sees and tells the narrator about, she is one of the people working in the Colonies, cleaning up nuclear waste.
The narrator is relieved at first to hear that her mother is alive—after she was abducted in the early days of the Republic of Gilead, she had little hope for her. But Moira thinks her mother would be better off dead. Living in the Colonies is like an extended death sentence. With the loss of both her mother and daughter, the narrator is completely cut out of her family circle.