Well, a little research will show that helmets do indeed increase the risk of certain injuries in motorcycle accidents, while reducing the risk of others, particularly if one opts for the full-face variety helmet. The thing is, the injuries that helmets prevent are far more common than the ones that they cause, so this argument advanced by Mr. Weir is rather foolish.
Helmet statistics are tough to read anyway, as a full-face helmet, an open-face helmet, a half-helmet, and those moronic beanie helmets that "tough guys" wear to meet the legal minimum are all entirely different animals. As an example, if you break down a full-face helmet into zones of likely impact in an accident, the most common point to be impacted is the chin area. Naturally, this isn't the case with the other types, as they don't have any chin protection...
By the way, Alexander, if I understand you correctly, her helmet was just a shell? If so, this was pointless, as it's the collapse of the inner material that cushions a blow to the head, not the hard outer shell.