She was mad at her friend and mad at her siblings (conjecture on my part based on the media reports).
I don't think that necessarily translates to mad at the world at large. Not with a 7 year old. I don't know if Somer was quick to snap at someone and quick to forgive.
A stranger might be just what she was looking for if he/she made the initial approach and was nice to Somer ... then Somer might respond the same way.
I just can't agree with your statement about knowing Somer did not go with a stranger that day.
Stats are on my side.