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She killed time reading magazines while she waited.
Literal
She [topic-は] is-waiting interval magazines [object-を] read-and idle-time [object-を] killed.
Two patterns chained. 待っている間 ('while waiting') uses 間 ('interval, while') after a ~ている clause to mark a span of simultaneous activity. ひまをつぶす ('kill time, idle away time') is a set idiom — つぶす literally 'crush, smash,' applied here to 暇 ('free time, leisure'). The verb chain 読んで...つぶした links 'reading' and 'killing time' as concurrent: she read magazines, and that's how she killed time.