Stephens finished third in her heat with a time of 2:13.26, but other heats were faster and she ended up 11th overall, with only the top eight of the 37 competitors going through to the final.
The second day of the championships brought yet more disappointment for fellow Leander swimmer Joe Hulme.
Hulme had missed out on reaching the 100m backstroke semi-finals on the opening day by just one hundredth of a second and then today he was disqualified from the men’s 200m IM, where he was expected to push for a final place.
However, Hulme will get a chance to make up for that tomorrow when he competes in the 50m backstroke.
Stephens and fellow Leander swimmer Tom Fannon will also be in the pool tomorrow.
Fannon will compete in the 50m freestyle heats and Stephens the 50m butterfly event.