Birthday Expedition is a Document in the Rise of the Tomb Raider: 20 Year Celebration DLC Blood Ties. It belongs to the Winston set and consists of a diary entry written by the Croft's butler Winston.
This will be good for her. She's been acting up of late, but I know she's just craving more of her father's attention. He's been so buried in his research. It will be a nice moment for the two of them to reconnect.And I do believe he needs it as much as she does.