Karen, I have noticed that the heads with neck rings sometimes do come off easier, and if the head is heavily weighted, and bounces around in transit, it could be possible that it did come off. I have only seen this propensity in the softer vinyls myself. I have a Linde Scherer doll that I have taken the head off quite easily and replaced eyes etc. a couple of times.
I imagine it would be very horrifying to someone that does not reborn dolls to have the head come off like that. Maybe now that the initial shock has worn off, you could talk to her and work out something, maybe a small discount, if she pays for the doll again and keeps it.
I’m sorry this happened. It is hard enough being a reborn doll artist in this economy.
Take care,
Kathy