S 'was' correctly used in the sentence? Why shouldn't I use 'had been'?

Is logic of the sentences correct? I think they are. Is 'was' correctly used in the sentence? Why shouldn't I use 'had been'? Amelia was 35 years old. Her being seven years old was 'more past.'

35-year-old Amelia recalled something. When she was barely seven years old, she learned that her mother had been killed in a city brawl. It had been 28 years since the murder of her mother.