I would think this might be a possibility with the zombie beholder. It wasn't even a full-strength zombie beholder, so maybe its eyebeam isn't the equivalent of a full-strength disintegrate spell.
I think what I'm going to do is offer my player three possibilities, each with a trade-off of PC coming back quickly versus PC coming back unchanged:
1. PC could come back very quickly but with a Dark Gift that will require a greater restoration spell to remove (the higher-level spell requirement is a reflection of the fact that the PC was disintegrated, not just dead).
2. The rest of the party could scoop up the dust and find a druid to cast reincarnate; the PC would come back with no negative effects but in a different body. In the meantime, assuming the player doesn't want to roll up a temporary character, the PC would be a ghost with limited abilities.
3. Player waits until the party finds someone who can cast true resurrection or wish, getting the PC back in her original body and with no negative after-effects. The player will definitely need to make a second character in the meantime.