Final answer:
The correct spelling in the sentence is 'rein'.
Step-by-step explanation:
The correct spelling of the word in the sentence is rein instead of rain. 'Rein' means to control or restrain, while 'rain' refers to the water that falls from the sky. Therefore, the correct sentence would be: 'The ambitious young manager was told that she would have to rein in her plans until profits improved.'
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