So, Natasha wants to reclaim herself, her life, as much of it as possible, and since she doesn't have real *memories* regarding Christmas (and if so, not many, not very clear ones); she can choose what she wants for this holiday. It might become even more important to her now when she's partnered with Clint and he doesn't seem to have many happy memories about it. In my headcanon he is usually nudging her in the direction of various things and promtping her to pick what she likes, and he loves showing her new stuff that's good and fun, and now she can return the favor and help him reclaim the Christmas for himself. It can result in funny things, hilarious things, tender and passionate things done together (says the eternal optimist who loves the holidays :D)