From what I know (friend's info, I don't have AW Gaia) and from what sanahtlig is saying I surmise that AW Gaia's added 'thing' for 2nd ability is not nullification (like one Atalanta has), but 100% damage reduction/cut.
In most cases it doesn't matter, but Water Rag with rage trigger applies water rst down, which actually makes AW Gaia take damage even with her 2nd ability up (unless you have additional damage cuts). Doesn't matter for this GO though.