"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.