Hmm, it's almost like Islam isn't a monolith!

Please educate yourself about how Section 2(a) of the Charter works:  what is relevant is the religious belief of the individual.  If a woman believes that wearing a niqab is a sincere requirement of her faith, no more is needed.  Indeed, if a Presbyterian woman decided that wearing a niqab was a sincere requirement of her faith, she'd be entitled to the same deference, because faith is personal, not decided by others.