" ... as to my father, I never in my life saw him so affected. Poor Kitty has anger for having concealed their attachment; but as it was a matter of confidence, one cannot wonder."

Even here we see how Jane is sweet and finds excuses for Kitty.
And I don't think that Kitty imagined that Lydia will elope with Wickham, it seems that they share things like this before , I don't think that Wickham is the only man that Lydia fell in love with.