Mako,
Knowing something and accepting it are two entirely different things. This is why the first of the twelve steps is admitting - as in letting the truth of our situation fully inside of our selves and our perspective. Her problem is the relapse. Your problem is accepting that you are powerless over her addiction. You surely know that you are powerless, but if you find yourself struggling against it perhaps you haven't really accepted it?
Having sponsored a number of men in their journey I have found myself in your situation several times. In my experience, when we care about someone else's sobriety more than they do, we render ourselves useless to them and risk our own sanity in the process.
The day will hopefully come when your efforts can support her sobriety - but she has to make that happen on her own. In the meantime, take care of you.
Best,
Eddie