[PvK]

Other ideas:

Blindness

Paralysis

Black Bow of Betulf

the missile weapon that kills in one shot

capturing her home castle

unliving summons

outnumbering with own summoned Vampire Lords

Liches and Bog Mummies can do similar things, perhaps better when they have high built-in protection, which can be harder to counter than etherealness

magic weapons (bypass ethereal)

Death summons (several relatively cheap and skilled warriors available with magic weapons included and no life for VQ to drain)