Thanos' snap is deconstruction which wouldn't work against a non-corporeal. Anything AP-based (i.e. the Power Stone) or matter based (i.e. Transmutation) also would fall flat due to Shadow Queen's AP and the fact she's non-corporeal. This makes it far more likely that the Shadow Queen would one-shot Thanos before he pulls out any useful hax like time manipulation or mind manipulation, either of which he's rarely used.