Well TBF Bridgeit and this is coming from memory so I may not be entirely correct but I seem to remember that when RF when to church at Balmoral, the first Sunday following Diana's death, the Queen was asked if she wanted specific mention of Diana's death during the prayers of intercession and she declined.
She made a public statement on the death of Mother Theresa who died just after Diana, having made no such statement on Diana's death.
There were things that weren't done because it wasn't protocol for example the flag being flown at half mast at Buckingham Palace. That said, despite the out cry that this wasn't being done, it was some time before permission was given.
Then there's the funeral. Again another unprecedented situation for the RF to face but it was pressure from TB as a response to public opinion that this would be as close to a state funeral as possible, without actually being one.
The Queen Mother's funeral plans formed the blue print for this as nothing else was available.
It is reasonable to say the Queen ignored Diana's death? IMO no but it is reasonable to say that she seriously mis judged 'her people' when it came to acknowledging it, which for a time she seemed very reluctant to do. Hoping perhaps that the funeral would be a quiet Spencer family affair and maybe too that she wouldn't have too make a statement about her former d.i.l. and mother to two of her GC.
If that was the case she was extremely niave bearing in mind that once the engagement was announced she became the most photographed woman in the world and rightly or wrongly, one of the most famous and talked about members of the RF.