Tamara Siuda, the founder of Kemetic Orthodoxy, author and Egyptologist wrote a blog entry about the Establishment of the Celestial Cow holiday celebrated on December 25.
Here is the blog entry: Winter holidays: This one goes up to eleven.
Since Aset is also the Celestial Cow (Aset-Mehet Weret), you could also incorporate Her into this holiday. Or as the syncretic goddess Aset-Nut.
Fiercely Bright One 