Ellen Howarth-Brown, the All-England intermediate 300m hurdles champion, was runner-up to Eilidhi Child (Scotland) in the Home Schools International at Cardiff.
The Chichester High pupil ran a personal best 42.57sec in windy conditions which places her fifth on the all-time British under-17s list.
Child equalled the British record with 41.98sec.
Ellen, who was third in the event last year, said: "I was really pleased. It was very windy but I was determined to stay closer to Eilidh than last year. I'm really thrilled to run faster than ever in those conditions.
"I am looking forward to racing against Eilidh again in the AAA Under-17s Championships at Sheffield in three weeks time.
Cara Paine (Hastings) was third on her international debut in 44.5sec.
Cara and Ellen won silver medals as members of England's 4x300m relay team.
Wade Bennett-Jackson (Worthing), an intermediate 200m silver medallist at the All-England Championships, was third behind Julian Thomas, the Coventry runner who pipped him at the national event.
In the high jump, Sarah Fielding-Smith (Downlands, Hassock) was fifth (1.60m) after struggling in the wind.
She won a silver medal at the All-England.
HORSHAM Blue Star trio Michelle Hodges, Rebecca Jennings and Emily Eastland made full use of home advantage at Broadbridge Heath to scoop five of the nine individual titles at the Sussex Under-13s Championships.
Rebecca won the long jump in a championship-best 4.49 and the 70m hurdles (12.6sec).
Michelle won the 75m race (10.8sec), then set a season's best by a Sussex runner with 21.0sec in the 150m. Emily won the 800m (2min.31.7sec).
David Wheeler, from Lewes, set the only individual record when he won the boys' events, high jump (1.47m).
Kieran Lewis (Brighton and Hove) scored a hat-trick in the 75m (10.3sec), long jump (4.68m) and 150m (20.5sec).
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