Claire Manton missed out on a national medal by three hundredths of a second.
The 14-year-old Brighton club swimmer was fourth in the 14-15 50m breaststroke at the ASA Age Group Championships at Sheffield.
Coach Nigel Currucan said: "It was a good effort, she was a whisker away at a high level. Claire has proved herself in Sussex and Southern Counties events, but in the last couple of weeks has stepped up in class. She did well to get 12th in the all-ages longcourse nationals."
Amy Kent, also Brighton, was tenth behind Claire.
Currucan has medal hopes for Claire's clubmates Garth Kates, 12, and Holly White, 13, in their 50m butterfly events on Friday.
Kates has been selected for a Southern Region training day at Aldershot next month.
Shaun Challis, 14, was the first Brighton junior finisher at his club's Pier-to-Pier race.
He was 22nd out of 75 in the men's race in an event which had 108 competitors.
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