You are spot on that its more than grief over Art. I've suspected that she is mourning the loss of her own sense of authenticity and privacy. She jumped into all of this and got more than she bargained for.
Speculation: she merged with Art's very strong narcissism, and came to believe (encouraged by Art) that she really was the chosen one, the golden girl, the only super-talent who could possibly take over for Art. Her grief is unhealthy and out of proportion unless she was in fact deeply involved with him in a relationship. Clearly she was still infatuated with him, and he obviously could be charismatic. He himself said he had treated people badly, and I suspect he would have had no reason to change his manipulative self-involved ways that late in his life.
What galls me is she acts like she is the
only one who is entitled to grieve. Nothing about his wife Airyn, nothing about Karen who knew him and was close to him for many years longer than HW was even on the scene. There's a sense of possession of him there that, imho, is delusional.
Just some speculations, that's all.