Thegreatoutdoors, your theory makes alot of sense and is pretty much what I am now thinking.
Although I have changed my theory so many times, but as I have a friend who is looking like she is an alcoholic and I have stayed with her before, and we have gone to bed, and I have heard her get up in the middle of the night for a while and then go back to bed, and in the morning I realised she has drunk the rest of the alcohol. So now I think that EC maybe have got back up after neighbour left or woke up after a couple hours, drank alot more, and then not being good mentally has possible decided to end it all and jumped off the cliff which doesn't look far from her house. Then when hubby and kids got there, he maybe spoke to the neighbour and they worked out she must have drunk alot and as he knows her, he realised that she wouldn't be in a very good state of mind and could have contemplated suicide, hence his and the police's quick reaction.
Another theory is she planned it, hence why she didn't go to GF, wanted to watch GF though, neighbours came over, she was drinking, neighbour made sure she was going to bed when neighbour left, she got up after neighbour left, drank some more possibly and then jumped off cliff or walked into the ocean, makes me shudder just writing it