Great find mdcmdc, and very significant. My theory is this (and all purely speculative):
Elisa suffers depression and often seeks time alone to restore her mind.
Marriage may be rocky and talk of leaving husband is a form of escapism for her. Perhaps he isn't around a lot due to work, leaving her to deal with the pressure of looking after 3 children which is no easy feat when mental illness renders you almost incapable of looking after yourself.
Maybe alcohol consumption is a characteristic of her downward spirals. This leads to my theory that the neighbours are aware of Elisa's state of mental health, and may very well have been in contact with husband to let him know they had seen her safely to bed after she had drank watching the grand final.
Elisa decides after appeasing the kindly neighbour that she is going to bed, and checking in with husband, that in fact she isn't done. Under the influence of alcohol, she impulsively decides to take a walk to clear her head and/ or enjoy some fresh air. Being without the children, she's a free agent. Maybe she even mentioned to husband that she might take a stroll to sober up, which would account for the earlier narratives regarding an evening run.
She grabs her phone which might be almost flat after the day's use and heads to the beach to listen to the waves that connect her so strongly to her beloved mother.
Doesn't latch the gate or forgets entirely to close it. Dog may be fast asleep and doesn't realise she has left until morning, when s/he becomes anxious and wanders off to look for Elisa and/ or morning feed.
Elisa arrives at either beach or cliff top path and is overcome with emotion. The pressures of daily life, missing her mother, her feelings of inadequacy over whatever she believes she is not excelling at. And remember, at this point we know Elisa has consumed alcohol, just not how much. But my key point is this - did she engage in suicidal ideation and then whilst under the influence accidentally proceed?
Being a prolific and passionate writer I tend to strongly agree that no note seems out of character from what we "know" of her. Accidental suicide would mean she did not prepare a note at all.
I'm guessing that with 3 children aged between 7 and 12, this is a household of early risers. Kids missed mum, dad wants to spend a day of rest at the beach house so they leave early to make the most of the day. Husband is concerned that he can't contact Elisa, but figures she is making the most of a sleep in without the kids.
Concern turns to alarm when the family arrives at Airey's Inlet because mum is not around, the dog is missing and the mobile phone is flat. Knowing the turns her mood can take and no doubt all the more anxious with 3 children worrying where their mother is, he calls local police to ask if there have been any accidents etc.
Sorry if post is too long, and hopefully it makes sense (it does in my head :thinking: )