Sorry but what she is wearing is not an hijab. It is an aerodynamic tight head covering more akin to a balaclava helmet designed to control wind resistance caused by longer hair, the thing even has a Nike symbol on it.
An hijab is a head scarf and there are strict conventions on what constitutes one, how it is folded and worn and how it is held in place.

Had this been simply a case of a jobsworth ruling I would have agreed that it was unfair, but the item is not an hijab it is performance enhancing sports wear and if that is against the rules of the competition, then they were right to disqualify her, doubly so for lying about it.