Here's what I am thinking as a possible scenario: SS wants to end her relationship with RS. She has begun and or resumed a relationship with X. X does not want her kid. SS would also like to end all her responsibilites. So she and he devise a plan to make it look like both have disappeared. Her recent lapses may be to convince someone she is still having a problem. But, there are few alcoholics who would leave a half bottle of wine undrunk in such a stressfully excusable in her mind situation. So I do not think she was actually drunk, but rather very nervous about what she planned to do.
Leaving cell phone. Leaving a high profile easy to follow path timeline would be her going overboard to convince that she merely became lost and that's why she ended up where she did. But, it is so far off that she realistically would have only found it if she had been there and knew this place and it was a designated rendezvous point. Why this spot? Well for one thing, I see from google earth that it sits on the mouth of about 6 different inlets/outlets and be much more difficult to ever find her or son's missing bodies. If her's is never found no one will be too questioning.
Leaving the van with doors open just LOOKS like it was meant to be flooded with water.
All her activities seem suspect to me.
I could of course be wrong, she could have been drunk or taking pills and just been disoriented like most people think. But, how could she navigate that road much less find it off someone's driveway?
Time will tell. But, this poor little boy is a victim no matter which outcome turns out to be true.