The newspaper article mentions the hair regulations. Why? Because the females guards must have their hair tied back in order not to obstruct their vision & to avoid entanglement for safety reasons. Ergo, the same principles are being applied to the hijhab in this instance as it restricts the vision and can also become entangles, and/or used as a weapon etc against this female. IE it is a safety hazard.
Hair regulations though, play no other part in this story andthe actual wording of the hair regulations is moot.
This this same woman very possibly has hair as short as mine under her hijab. It is also a matter of my experience with Muslim women as well, that most also have plenty of expertly applied make-up underneath those hijabs. To her, it is not a matter of not wanting to conform, it is a matter of her religious beliefs.
Although not all Muslim women "must" (or are obligated to) wear the hijab, it is a matter of the extent of their devotion and is a sign of their faith. Much the same way as some of the more devoted Catholics etc will attend those masses daily, rather than show up just for confession on Sunday. Comments that they shouldn't wear them "because they don't have to" are inappropriate. You would never say "Catholics can't go to daily mass because they don't have to."
In this case however, the decision has been made because it has a direct impact upon her personal safety and therefore IS the proper decision under the circumstances.
Whether she signs a waiver or not is also a relatively largely moot point. Even if a waiver was signed, you can bet your butt that should something ever happen to her after it was signed, the Provincial, Federal, Municipal employer would indeed still be on the hook for willfully & knowlingly placing this pers in a situation where her personal safety could not be ensured, probably sued, and more than likely found culpable. Waivers or not, you will find that the Canada Labour Code expressly forbids employers from putting employees into a situation which may compromise their safety, ergo the employees "right to refuse."