When something like this happens, people like to have someone or something to blame. Drugs? Intruders? I see many things in this case that Ada may have been withdrawing from life herself. We've all heard of her plan to ditch her condo, we know that she had stopped working, we know that she volunteered to be up at the cabin. We also know that she didn't come home with the BF, even just to visit her son. We know that she spent god knows how much time calling multiple people, and talking for almost five minutes, yet never once called 911. The know she gave the wrong address. We know that despite being in a locked cabin, armed with a gun and extra ammunition, she made the decision to abandon the very things that were protecting her.
In my opinion this is very likely a suicide. One of the negative aspects of taking ones own life is that the ones closest to that person feel guilt and a lack of self worth. I believe Ada concocted this abduction idea in an effort to spare her loved ones these feelings. I believe she made the call from inside. I believe she purposely gave the wrong address so she would know exactly when the police would be close. I believe she sat on that roof, a place that we know was her "peaceful" spot, for some time. Then she abandoned her phone and gun and simply walked to the pond and ended it.
Yes there is the possibility of a drug induced event or a complete mental breakdown, but is there any real evidence of drugs? Has she ever had any kind of mental episode before? Again, its possible, but IMO unlikely.