So rather than Orm and his fellow pure Atlanteans still going about their business instantly upon exposure to air, they need to get that water out of their system before doing anything else.
She does so by opening up a patch of air underwater, and when Orm lands inside of it, he’s briefly incapacitated and starts throwing up water.
This doesn’t sound anywhere near as disgusting as the vomiting sequence from Blockers earlier this year, but it’s nonetheless unsettling, not to mention scientifically sketchy.