I love that picture above.
I have to admit that I was thinking the same thing about her being in the Chariot with a helmet on. If the crash is big enough that she needs a helmet to protect her head when she is in the Chariot then the helmet would be of no use anyway.
This topic came up on the Fredcast / Spokesman podcast the other week. David, the show presenter, saw someone pulling a Chariot in traffic with the the small occupant not wearing a helmet. He thought that the parent was being hugely irresponsible not equipping the child with a helmet. While it might be reckless riding in that environment if parent and child are hit by a car helmets would be of limited use.
I have already done numerous (and very careful) miles with a helmetless daughter in the chariot behind my bike and you are right, she was out like a light within minutes.