The witch is surrounded by the enviroment she is in, so of course the environment touches upon her and she touches back. Holidays are not the center or root of a witch's power. That comes from her connections and skills. The work gets done when the energy is right by FEEL and MESSAGES given by the powers that be, and there are four seasons in which to do these things a witch does.
Simply stated, I grew up celebrating Christmas with my family and I see no reason not to continue having a tree, presents, candles, music, and a ham dinner, just because I found out over the years that I was being contacted with forces that wanted to get to know me and work with me.
Just becuase I am a witch, that doesn't mean I have to decide to ignore perfectly good opportunities to have celebrations with my family and friends in order to pick another day and then try to recreate some new religious pattern with minimal real-life continuations to back it up, just because that's what modern witches are supposed to do! Lol!
I go with the energy! Invite me to your celebration, and whatever religion or lack of religion it is from, I may come for the party and friendships, but don't expect it to be the basis of my witchcraft. Because that was taken care of already.