Humphrey ran her lifetime best 100m hurdles time of 12.83 secs to win the second semifinal at the 1988 US Olympic Trials, before going on to win the final later the same day in 12.88, to defeat Gail Devers (12.90) and LaVonna Martin (192.93) and earn Olympic selection. At the Seoul Olympics, she ran 13.24 in the first round and 13.25 in the second round (quarterfinals) to reach the semifinals, where she was eliminated running 13.59. At both the 1992 and 1996 Olympic trials, she missed out on the semifinals by just one place.