I'm not going to dismiss the blackface in the slightest but her not realising how totally unacceptable that was might just be a generational thing.

(Which is still unacceptable but I wanted to understand if she was just really ignorant or indifferent or what, so I did a bit of digging to understand if it was something related to culture and age.)

I'm totally speculating but from what I know of the TV and general comedy that played in the U.K. in the 70s/80s, there was blackface on TV now and again; I can name a few shows that I know either parodied that entire situation or included it. Particularly The Black and White Minstrel show (yikes). Unfortunately I know of a number of people in their 50s who thought it was harmless humour that everyone could find funny despite it being at the expense of black people. And perhaps that's how Charlie perceived it, your standard offensive humour but assumed that others would find it funny. (Yeah no.)

Growing up in those times when blackface was more acceptable and therefore not understanding precisely how offensive it is was likely a contributing factor. Her apology was genuine and that still obviously doesn't make it okay but there's a little bit of a difference between blackface that comes from ignorance and blackface that comes from malicious intent.

TL;DR - Growing up when she did was probably a contributing factor to the lack of understanding behind the blackface.

The research was a product of boredom one night after watching a series of programmes akin to 'It was Alright in the 1970s' and I wondered if it was applicable to Charlie after watching 60-70 year old comedians say 'well, that's what people laughed at back then'.