Hi! :)
I saw your comment on my story and I thought you might want to know my reasoning. Firstly, like in everything in TVD, magic has it's loopholes. This is one of the only loopholes that could be used in hybrids. It's not natural for a vampire-werewolf hybrid but it happened anyway. Next, Arielle's magic doesn't actually come from the earth-it comes from herself. She's not bound to the earth like other witches are and this is not only because of her bloodline but also because of several other reasons I can't give away for fear of too many spoilers. Just know that Arielle's magic is her own and though she can, she has no need to channel other's magic because of this. It's almost like having the element spirit. It comes from within her instead of a natural force. Does that make sense?