Exact same issue here. The Dragon does the purple beam attack, Maia's HP is reduced to 0 but does not die, or take any more damage. I finished the DLC and got back onboard my ship, swapped her out and then back into my party, still had the issue. Even after reloading and all that jazz, she's still stuck in a zombie state.
Can verify that nothing seems to reset Maia to normality; neither resting, removing & re-adding to party, nor saving and loading.
Anyone tried a save editor or similar?
Also, interestingly the Life in Death healing aura from the Blackened Plate Armor deals NaN damage to Maia every tick now according to the combat log and the floating combat text says -2 147 483 648.