Catrina McDermott has been threatened with expulsion for wearing emblems of St Patrick and the guardian angel.
If a school has a rule about keeping the school blazer free from any sort of badge she should be prepared to accept and keep that rule if she wants a place at the school.
It's not religious discrimination at all. If the girl had gone to school with skull and crossbone pins or band badges on her school blazer and was protesting about a suspension, you'd be saying she should grow up and wear her proper school uniform. This is no different.
If you had a job where you had to wear a uniform, and a condition of that was no jewellery, you'd have to stop displaying it.