I found a solitary vegetarian Percy Pig in a cupboard and ate it in honour of this thread. 
The other thing, as well as the mad meal timings, that struck me about the start of New Mistress is just how mentally young Kathie is portrayed as being. I get that EBD was essentially using the 'new girl' model to introduce her new mistress, but Kathie does feel like a total child at the beginning (for a 22 year old graduate who has persumably just spent three years away at university), wanting her aunt to open the CS acceptance letter for her, tumbling down on her knees beside her aunt in a way EBD usually has children doing, declaring that she's going to buy all her own clothes for the CS as though this is a first, telling Biddy that controlling a classroom 'doesn't sound awfully easy'...?
I know we're supposed to feel that she's essentially a good egg, like one of the 'good' new CS girls who just need some corners knocked off before they're 'in the mould', but it did make me wonder why the CS, which presumably has its pick of applicants, would choose someone without the slightest life or professional experience (and without teacher training, unlike some of the other younger staff like Sharlie Andrews, who came through teacher training college rather than university)?
Presumably we're to imagine that the CS likes to get its teachers very young and mould them, so they don't rock up like the unfortunate Miss Bubb, with wild ideas of their own (like prioritising the school's academic performance)? 
Mind you, Kathie is clearly some kind of linguistic genius, as she appears to have acquired French and German fluent enough to teach in without doing a modern languages degree (at least I assume not, given that she's hired as a maths and geography teacher, so I assume her degree was in one of those?) and without ever leaving the UK, apart from two holidays in Brittany and Normandy?
So that's why they hired her!