Oh, I think we can have a guess at what the Queen thought. If the original BBC report of 2021 was from a Palace source, and that source did not corroborate H&M when they were threatening libel against a number of media outlets including the BBC, I think you can be pretty sure that she was not amused. And none of this was mentioned in Spare, nothing about a phone call to his dear granny to ask for permission - funny that. Besides which, if Hardman's book hasn't been lawyered up to the hilt and contains libellous inaccuracies, they can still sue.
The Queen being "the angriest" she's ever been. Ever heard of death by a thousand cuts? After what several of her children and one of her grandchildren had put her through over the years, together with her beloved husband dying, maybe this was just the straw that broke the camel's back. Everyone has their limits.