Halsall was put through the mill on the second day of two in Scotland, winning the 50m freestyle to give her European team full points before turning her attentions to the relays.
The 23-year-old then combined with Michelle Coleman, Jeanette Ottesen and Femke Heemskerk to win the women's 4x100m freestyle relay in a time of 3:27.70minutes.
But, with the scores level at 131-131 after all of the scheduled events, Halsall wasn't done and anchored the European 4x50m mixed medley relay quartet in the deciding tie break.
The team of Halsall, Ottesen, Chris Walker-Hebborn and Damir Dugonjic couldn't pull off the win though as Eugene Godsoe, Kevin Cordes, Claire Donahue and Simone Manuel came to the fore.
The American quartet produced a world record time of 1:37.17 to touch out the European Allstars by just 0.2seconds and triumph overall having overcome a significant deficit from day one.
And an emotionally drained Halsall, who won Britain's only medal of this summer's long course World Championships in Barcelona, insisted the European team could be happy with their efforts.
"It's been a tough day," said Halsall. "We were ahead but we knew it was going to be touch and go as to who would win.
"It came down to the freestyle relays and the girls really got together as a unit and swam really well and broke the world record.
"That was fantastic to be a part of and I was really buzzing after that. I knew I'd have to calm back down and get ready for a swim-off and that was hard and emotional but so great to be a part of and I really enjoyed it.
"Standing up as a European team and being that close to the Americans with so many people behind you is something I will be proud of for a long time."