I reckon it's the other way around- Gaia gives her the opponent's power +1, but that's only at the beginning, when it goes "kay, castle's materialised, go out into the world, your target is here someplace, here's x+1 power." Then it just refills her as she uses up the power. Because your way, Gaia would be adjusting her vampiric impulses along with the power it gave her.
But I suppose we can't really argue over this, we don't have any specifics. Down to personal opinion til Nasu says otherwise.