Overholt, of West Vancouver, B.C., finished the freestyle race in a Pan Am record time of four minutes, 8.42 seconds.
Venezuela's Andreina Pinto earned silver in 4:08.67 while American Gillian Ryan placed third in 4:09.46.
Overholt, the youngest member of the Canadian swim team at 17, out-touched Caitlin Leverenz of the United States at the wall to finish first in the 400-metre individual medley on Thursday, but she was disqualified for a "non-simultaneous" wall touch during the breaststroke leg of the race.
Victoria's Ryan Cochrane cruised to gold in the men's 400 freestyle by a margin of over a second.
Cochrane set a Pan Am record in finishing the race in 3:48.29. Ryan Feeley of the U.S., was second in 3:49.69 and Leonardo De Deus took bronze.