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She kept the child shut in the room until they stopped crying.
Literal
She [topic-は] child [subject-が] stop-crying [until-まで] room [in-に] shut-in.
A harsher snapshot of parenting. 泣き止む ('stop crying') is a compound verb stitched from 泣く ('cry') + 止む ('cease, stop') — the second verb often pairs with a first to mean 'stop X-ing': 雨が止む ('rain stops'), 泣き止む ('stop crying'), 笑い止む ('stop laughing,' less common). まで ('until') marks the time-point endpoint. 閉じ込める ('shut in, lock up, confine') is built from 閉じる + 込める, with 込める adding the 'into / in' direction. The に here marks the location of confinement.