Competing at the event in London, Neath-born Brier broke the long-standing Welsh record with a time of 22.79, underlining her status as the fastest Welsh woman of all time.
The record of 22.80 seconds had stood for 44 years, Michelle Scutt having run that time in Antrim in 1982.
Brier, 28, also holds the Welsh 100m record of 11.26 seconds, which she set at the same Stratford meeting last year.
The Swansea Harrier recently set a new Welsh indoor 200m best, producing a time of 23.25 at the UK Athletics Indoor Championships in Birmingham.
Brier almost quit athletics in 2024 as she struggled to balance her job as a council youth worker with a demanding training routine.
A member of Team Wales as a 16-year-old at the 2014 Glasgow Commonwealth Games, Brier also competed at the 2022 Games in Birmingham.
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