It's interesting, and I don;t wish to assume anything here - let's face it, that behaviour is what's generated this post in the first place - but I am willing to bet, and do correct me if I am wrong, that all those who are inferring that this is fuss about nothing, are all white British.
As the lady in question has pointed out, as parents of immigrants, she has grown up experiencing violent racism as a daily occurrence, and it's likely that it has made her somewhat sensitive about instances of it in her life, regardless of whether they were 'intended' or not.
Of further interest, is the defence of the cuplrit, on the basis of her age, possible autism, senility, and so on, as though because she is old, appalling bad manners are acceptable.
They are not.
Her age, experience and position, should have made her less ignorant of social graces, not more, and if she is unable to conduct conversation with people without arguing about her bigoted assumptions, she should not be in public, never mind at a palace function.
As far as I am concerned, defending the finer points of whether her attitude was 'racism' or 'ignorance', is rather like arguing about domestic violence - he didn't punch her, as such, he just slapped her, as though that somehow makes it excusable.
Regardless of the lady's explained sensitivity to racist attitudes, simply as a guest at a function, she was subjected to rudeness and offence from a bigoted reactionary old biddy who thinks all 'darkies' are 'foreign', and she has the right to know where they have been brought over from.
It was unacceptable, and minimising it or explaining it away as simply being the result of age and a 'different time' is simply not good enough.
Ignorance and bigotry are defeated if we call them out, not if we simply smile and shrug our shoulders, as several on here are keen to do.