Some nice warmish water a few inches high sounds good. Some people say their hens end up relaxing and falling asleep in the warm bath. If you can't pull that egg membrane out after she has soaked in her bath, then you can use the dropper to put a little clean warm water in her vent.
Well if she has any more soft shelled eggs in the future at least your will have an idea of what to do.
Well if she has any more soft shelled eggs in the future at least your will have an idea of what to do.