Jealousy - probably about having a 23" waist
but class regarding the names of her kids, her top from primemark, the bad highlights, looking a minger, chav - these words are all associated with a certain class of people. Thats why inthink it is an inverted type of snobbery.
As for me - I've grown up middleclass, then lived in a council flat, married, then single mum, then own business and own a couple of house so been on both side of the tracks. Probalby just inbetween I suppose but never really thought about it.
But the whole point this mum may be a member of mumsnet - she has lenty of kids to qualify - and i'm horrified that long standing members seem to have forgotten mumsnet's philisophy.