CPR
The time when someone held on her hands and dragged her to the surface, she already lost her consciousness. Riggs instantly dragged Seraphina to the awaiting yacht where X was waiting for them.
Earlier, since Leon's massive distraction, it caused a whole stampede and a terrifying panic to the whole area making it harder for the authorities that were chasing after him to catch up. When suddenly, X voice went through his earpiece saying he needed to jump off the bridge as well as they were reminded that the river's sea level sometimes arises and Seraphina might not make it.
Surely, X statement was spot on as he was also monitoring every little detail of their location -- even the water current and the how many civilians and authorities present.