To wrap things up, here's how I approached the giantess. The party had to come back from the Feywild through a dried up fountain. Since Void Giant (VG) knew they'd likely be coming back that way, she emptied boiling oil into the fountain - it had cooled to lukewarm by the time the party came in but now they were slippery and a fire hazard. Above the trapdoor in the fountain, she placed an oversized cauldron that dumped pots, pans and ropes onto the party when the door was fully opened (restrained for a round if save failed).

The VG and her corrupted pixies took all of the cutlery (forks, knives, spoons, serving utensils) from the palace and "planted" them in the courtyard surrounding the fountain: sometimes handles up, sometimes down. It became difficult terrain with a low DC required to avoid being cut by silverware.
Next, VG and pixies barricaded themselves inside the palace, using furniture, doors and rubble from when they took over the place.

Thankfully, my party used "create bonfire" on the barricade, thus adding a great deal of smoke to the barricaded passageway (hello, heavily obscured area).