、。
She'd been setting aside a little money each month, in preparation for retirement.
Literal
She [topic-は] retirement [for-に]-preparing-and, every-month some [each-ずつ] money [object-を] was-saving.
~に備えて ('in preparation for') is a fixed pattern — the te-form of 備える ('prepare'), used adverbially to describe action taken with a future event in mind. 毎月いくらかずつ stacks three pieces: 毎月 ('every month'), いくらか ('some amount'), and ずつ ('each / per portion'). ずつ is the distributive particle, marking the per-unit allocation: 一日に一回ずつ ('once a day each'), 二人ずつ ('two at a time'). The combination ~ずつ + ~ていた describes a steady, ongoing accumulation. 貯える ('to save up, store') is more formal than 貯金する; the kanji 貯 ('store, accumulate') signals deliberate hoarding.