I am so very sorry for your loss. Having lost my mom after a long period of illnesses incl dementia I understand. As you state, let's not assume, or judge. You may be projecting your own experiences onto this situation. The neighbour spoke to police and media afterwards, and was clear and concise. So perhaps not suffering of any ailments.
I just thought about how if this was my child, sister, friend, I would have so wanted someone to come in and help, step up and call it in. And that, is also projecting my own feelings and experiences onto this situation. My bad.
With hindsight everyone wishes things went differently, or they had acted differently. I just hope she is found. Soon. The poor kids, this must be soul destroying.