12 days of Christmas

My sister has just sent me a parcel containing 12 small presents. The idea is to unwrap one a day, starting on Thursday with number 12 and finishing with number 1 on Christmas Day itself. I've already guessed that number 1 is a chocolate orange so that won't be waiting until the 25th.

But, hasn't she got it wrong? I thought the 12 days of Christmas started on Christmas Day and went up to 12th night on 5th January?