"Experience kills innocence"

In his poems, William Blake describes Innocence and Experience as two contrary states of the Human soul, both important and inseparable.
I think that to interprete those poems and Blake's warning us that it's not possible or desirable to choose between both states of Innocence and Experience, it was necessary for Rita to have been in such states at a particular time and that was what has happened to her.
Whether we like it or not, we grow old and as a consequence we leave innocence behind because we come to know through new experiences of life, for the better or the worse.
Rita is no longer innocent; she had new experiences, some bad like her splitting up from her husband and some others good like her achievements at summer school which let her grow up.

Chickening out?

Rita didn't go to Frank's dinner party because she felt that she did not know how to behave well in a party where she would meet people with a higher level of knowledge than hers.
Neither did she know what to say nor remembered anything about what she had learnt. Moreover, she did not know what dress to wear and what sort of wine to buy.
Anyway, after a long journey because of taking the wrong bus, she could get there. However, she did not dare to come in. She seemed to be very disappointed.

The importance of learning a language

Rita used these words to express her enthusiasm for Macbeth:
"I thought it was gonna be dead borin'...
But listen, it wasn't borin' , it was bleedin' great honest, ogh, it done me in, it was fantastic. I'm gonna do an essay on it".
Of course, her language is not acceptable to do an essay. In the past, in England class was determined by the way people spoke but even more important was their accent. For example, people with strong accent like Rita's were assumed to be working class while people with RP accent was assumed to be upper or upper-middle class. However, then it was acceptable to speak standard British English in public speaking, radio, TV, books, newspapers, at school and university. That is why she is supposed to learn standard English. She must learn British language and how to use it in certain circumstances, that is in context.