Halsall helped herself to an excellent start in her 50m butterfly final, but only just held on for gold ahead of Australian duo Guehrer and EmilySeebohm.
But the 22-year-old picked herself up to win silver in the 50m backstroke event later on Friday, finishing just 0.03 seconds behind Australia's Sophie Edington, while Davies and EmilySeebohm of Australia could not be separated for bronze.