Come to think of it, I wonder if anything was missing from her home- articles of clothing, suit case, etc. Strange that some things were left behind.
I still feel foul play is involved. It may not have happened at the house. An old acquaintance or friend could have dropped by unexpectedly and asked her to go for a quick walk or ride with them, maybe saying they needed someone to talk to. So, if nothing shows up at the house, it's still possible that she was harmed, but elsewhere.
Unfortunately, there's a lot of savvy criminals out there lately. Many know about DNA and forensics.