There is clearly more to this than first appears.
On face value, it appears that the teacher is being unfairly treated for exercising her personal religious beliefs.
But the link advises that she was dismissed for refusing to adhere to school policy.
Now we all disagree with aspects of the ways our jobs require us to behave, but if we are contracted to adhere to those aspects, and choose not to adhere to them, then the consequences are followed - and that appears to be the case here.
I suspect the tribunal will side with the school, not because the teacher followed her personal beliefs, but because those beliefs caused her to act against her employers' contractual obligations, and that is why she was dismissed.