+1. The Meteor store manager (rightly) figured that if they kept up the bluster long enough, you would eventually say "ah feck, thirty euro to make the problem go away..." and let them off the hook.
Moreover, despite failing to uphold their obligations under consumer law, Meteor will make a lot more profit from your sister between now and March 2016.
This is why they try this kind of mullarkey so often — because they get away with it. My son has worked in a mobile phone store and says you wouldn't believe the egregious lies they tell people, both when selling them new phones and contracts and when wriggling out of warranties.
At the very least, your sister should write back to Meteor and tell them that that their stated reasons for refusing to honour the warranty have been proven to be false, that they have broken the terms of their contract with her and that she wishes now to be released from it without penalty or she'll refer the matter to her legal advisors.