Looks like your sister benefitted from the special service which exists in Derry. It doesnt surprise me that they reopened a desk - I even know someone who called when his car broke down. As he was flying LDY - DUB 3 or 4 times return a week, they knew him and asked the captain if they could hold to the last minute for him. They were standing at security with his boarding pass and got him on by the skin of their teeth.
Looks like they did something similar for your sister given the plane was there and her luggage was through checked.