Is the deceased father of my client attached to her, as I see intuitively? Is this a factor in her current feelings of sadness?

Both of these things are true, and you have seen to the heart of the issue as well in understanding why the father failed to transition successfully at the outset. It was his struggle with faith and his anger towards God that set him up to have misgivings. So rather than lean on strong inner faith that he would be loved and accepted back in heaven, it created doubts within him about his own personal standing and acceptability. That was enough to cause fear that took him out of divine alignment. And with his difficulties towards the end, as his life was narrowing down his options, his happiness, and the possibility of a future, he was cast into the darkness through his own inability to maintain a high enough vibration to see the light callers coming to greet and escort him back home. His thoughts of his loving daughter were the only thing he could count on. This not only sustained him, but caused his energy to seek her out, and in wanting to be with her once again he did catch up with her energy, and seeking that closeness, was invited in by her deep subconscious. This was not a clear perception, but a dim one and enough to see the father was troubled. And as she was grieving his loss, this added to inner sadness within the deep subconscious and this emotion was being ramped up by its effects on the body, because emotions are the only way for the deep subconscious to communicate, as it cannot interact with conscious awareness directly. But that is a weak and nonspecific signal at best. And she, of course, had no way of knowing all this was going on, but was feeling an impact from it. Your work with the Lightworker Healing Protocol, by attending to the removal and healing of spirit attachments, will take care of his plight and help him return safely to the light once again. And both parties will be blessed with this happening because otherwise, his troubles would continue to rumble within her and keep her off-balance. He will be in a better position to see and interact with her and hear her thoughts and messages directed to him, than would be the case where he attached to her energy in a very diminished and incomplete state of being, as a soul projection without a body.