Just curious, why do some think this was some diabolical murder scenario? Having even a little to drink, swimming in rough waters at night could easily cause someone to drown.
Since you are asking
Simply because , a Girl like her ( unless she is an Olympic Swimmer who loves Challenges)
, does NOT go for a SWIM in a ROUGH OCEAN ......ALONE , with him Passed out Drunk on the chair ,.
Which would be AFTER he just got tossed by a wave , hard enough to Throw up on himself ( his words)
Or was he in the water with her at same time ? when , before he got tossed , or after ?
There are not many other Scenarios
Not challenging you
but try to write out a Scenario where her Entering the water and drowning, and no one including him ,has any idea she just got sucked out to sea .
Sketch it out .. it wont work