It doesn't come across as any kind of a sneer at Donna Air, it read to me as a sneer at James Middleton. LH said 'could you imagine him going out with a girl who worked in Dorothy Perkins?', suggesting that James Middleton wouldn't 'lower himself' to date someone so low down on the social ladder, as he thinks he is above that. I really don't see how people in any way are confused about LH's post? It was very clear.
I have to agree not one part of what LH said (BIB) refers to Donna. So how people jumped to the conclusion that its was about Donna is behond me lol