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She makes a point of always remembering each of our birthdays.
Literal
She [topic-は] we one-by-one [of-の] birthdays [object-を] without-fail remember [make it a habit-ことにしている].
The pattern ~ことにしている expresses a self-imposed rule or personal policy — 'I make it a point to / I make a habit of.' Built from ~ことにする ('decide to do X') plus the ongoing ~ている, it frames the behavior as a maintained personal commitment rather than a one-off decision. Note the reduplicated 一人一人 ('one person, one person' = 'each individual'), a productive pattern for distributive emphasis (一つ一つ 'each thing,' 日々 'day by day'). 必ず ('without fail') intensifies the conscientiousness of the habit.