The first sign of trouble came early this month when Carol didn’t show up for her shift at John’s Waffle and Pancake House.

She was as reliable as the sun rising over rice and melon fields in her adopted hometown, Kennett, Mo., a conservative farming hub of 10,000 people in the state’s southeastern boot heel, where “Missouri” becomes “Missour-uh.”

In the 20 years since she arrived from Hong Kong, she had built a life and family in Kennett, working two waitressing jobs and cleaning houses on the side. She began every morning at the bustling diner, serving pecan waffles, hugging customers and reading leftover newspapers to improve her English.

“Everyone knows Carol,” said Lisa Dry, a Kennett city councilwoman.

That all ended on April 30, when federal immigration officials summoned Carol, 45, whose legal name is Ming Li Hui, to their office in St. Louis, a three-hour drive from Kennett. Her partner, a Guatemalan immigrant, had voiced suspicion about the sudden call. But “I didn’t want to run,” Ms. Hui said in a jailhouse phone interview. “I just wanted to do the right thing.”

She was arrested and jailed to await deportation.

Ms. Hui’s detention has forced a rural Missouri county to face the fallout of President Trump’s immigration crackdown, which was supported in theory by many residents in this Trump-loving corner of an increasingly red America.