The aircraft carrying her came within three miles of a military cargo jet, rather than the minimum five-mile distance set by US aviation officials.
The Federal Aviation Administration (FAA) said the planes "were never in any danger". Both landed safely.
The FAA is investigating Monday's alert as a possible controller's error.
It was the latest in a series of episodes involving apparent lapses by air traffic controllers.
Several controllers and supervisors have been suspended by the FAA since late March over incidents involving workers sleeping on the job, almost all of them during overnight shifts.
Another controller was suspended on Monday for watching a film when he was supposed to be monitoring aircraft in Ohio, the FAA said.
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