'Who cares for you? You're nothing but a pack of cards!'
-- Alice, to the Queen of Hearts.
There's always a way. For the setting or the campaign to be worth playing, there has to be one. Otherwise, it's not D&D anymore - it just devolves into childish I'm Rubber, You're Glue situations.
But how? Take your pick of the following.
Bag of devouring either tossed over her or her tossed into it. Whatever goes in doesn't come back out. Period.
Mirror of opposition. Whatever arbitrary, dice-less, stat-less uberness the 'lady' is meets its intractable opposite and is negated. Either they are simultaneously destroyed or this creates some kind of black hole singularity. And on that topic:
Paragon Umbral Blot. The rules for this (and there actually are rules for this) state that whatever it touches is annihilated. Only the direct intervention of a deity can prevent this, and it seems inferred that the Lady is no deity. Blots are referred to as 'assassins of the elder gods', which might mean they worked on behalf of those beings, or subsumed them into absolute nothingness. Or both. Blots can't even be selected as targets of effects, as they are not a presence but an absence. Only three spells in the entire game do anything to one - they're expressly immune to any other effect.
There's lots of ways. Tuerny's Flask (from AEG) loaded with archfiends. An epic Spelldancer exploiting their 3E loophole to end up with 'infinity' as root attributes. Or just the reliable talisman of pure good which allows no save and lasts forever. The point is that a setting that needs an omnipotent hyperbeing to be made to work simply doesn't work in the first place.
