The queen loves Meghan and invited her to Christmas before she married into the family
The Queen’s Christmas celebration is reserved for royals only, Kate for example spent the holiday with her family before she married William. But the queen seems to be very fond of Meghan since she has made an exception for her. She invited Meghan to spend Christmas with the royal family in Christmas 2017, before she was married to prince Harry. Prince Harry probably had influence over the decision as well, he probably told the queen that things are serious between the two and they’re going to get married soon. He might have added pleeeeeaaase!!