The City of Liverpool sprinter returned from a four-week camp in Florida and 48 hours later posted a time of 54.53 to win the Burns Open Meet in Sheffield on Saturday. Her previous national best had stood at 54.56.
Halsall, who is coached by Colin Stripe, had spent her time in Fort Lauderdale with Ben Titley's Loughborough-based training group and there were other impressive results from his swimmers.
Caitlin McClatchey won the Women's 200m Freestyle event in 1:58.57 and Liam Tancock took the 200m IM title in 2:02.01.
The results delighted Titley at this stage in the season with Olympic qualification on the horizon at the British Championships at the end of March.
"Our camp in Florida went very well and these impressive mid-season results are a reflection of that," said Titley.
"We only arrived back on Thursday so to get to Sheffield and produce these kinds of performances is pretty special.
"The fact Fran broke another British Record is a testament to herself and to the City of Liverpool programme under Colin Stripe who is creating the next generation of world class athletes in Britain."