Will Elizabeth find true love, while sticking to her principles? (Pride and Prejudice)
Will Briony ever be able to make amends? (Atonement)
Can Jennet balance the demands of her husband, her children and her art? (An Equal Stillness)
Yes, it makes them all sound like a trailer for a B movie, but it does capture the essence of the books, the 'what it's really about'. In fact, thinking about it, the blurb for Adultery for Beginners used the question format: Can an adulterous wife be a good mother? which neatly encapsulates the theme.
Pitches are so hard to do - it has to be worth a shot at least!