。
Mother wasn't a good mother.
Literal
Mother [topic-は] good mother was-not.
Notice the redundancy: 母 (mother) as topic, then 母親 (mother) again as the predicate noun — acceptable because the first is a term of address/relation and the second is the categorical noun ('a good mother' as a type of person). The negative past copula ではなかった is the plain-form version of ではありませんでした.