One of the things I love about Lissandra is that with her kit, movement, and demeanor, there are SO many different skin ideas that would work well with her. I always thought that the first skin after Bloodstone would be either be a Forest or Atlantean theme. Other themes that I personal though would be cool is some sort of Volcanic Lissandra, Arcade Lissandra, Stormfront Lissadra....
But back to an Elderwood/Blackthorn Lissandra.
All your ideas are great, but I'm not a big fan of the whole totem pole idea. I picture either a tree where you can see the roots spreading out (like her ultimate does) OR a series of vines engulfing the person and spreading. When I picture Lissandra in this fantasy, I see her as a manipulator of nature, so the totem pole is not really working it for me and the theme.