Krk is a massive tourist area with beaches. It's also possible that she drifted out to sea on a paddleboard or raft and suffered a shock while trying to get to safety.
Regarding the comment that the area was "inaccessible". Virtually all beaches in Croatia are extremely rocky and razor sharp. Every beachgoer needs rubber soled shoes or the stones will cut your feet. So in that regard it doesn't make the story more mysterious, as just drifting 20m from a public beach can land you in even rockier areas.