No, mama is in the N/N class and although it's animate, it's one of a small group of animate N/N nouns that use y and z with possessives. Most of these words are words that express relationships between people.
mama = mother
baba = father
ndugu = sibling
kaka = (older) brother
dada = (older) sister
rafiki = friend
adui = enemy
Mama yake alisema = His mother said
Mama zake walisema = His mothers said
And if "of" is the proper translation for "na" in this case, why is "of" not one of the listed possible translations for "na"? I would have chosen "of" or "by", if either had been a choice, but since neither was, I though my understanding of the translation was wrong, and chose one of the words listed, "and", only to find that my original translation was right, and what I typed as a result of the available choices in the definitions, was wrong!
Instead of the simple past, like English uses, I am guessing that Swahili here would use the -me- tense, which is for actions that happened in the past, but the results are still there effecting things in the future. They don't say "The chair WAS broken" if the chair still is broken. They say that it HAS BEEN broken: "Kiti kiMEvunjika" (or kimevunjikwa??) So I am guessing "He was bereaved" would translate, "Amefiwa (na Mama yake)".