"Prim, proper, priggish, prudish, puritanical, Fanny simply couldn't deal with the threat of adult sexuality."
That's right, kids. Fanny wasn't upset that Edmund was all set to marry a woman who openly mocked his career and his religion. Fanny wasn't upset that Henry seduced and abandoned both her cousins and made them miserable merely for his own amusement. She wasn't upset that the play was not only considered inappropriate by the mores of the times, except in the spoiled upper classes, but that everyone was using it as a way to carry on illicit romances, or that it would be going directly against the wishes of the guy who owned the house. She wasn't bothered by Henry's near-stalker behavior towards her, or the fact that despite claiming he wanted to marry her, he promptly ran off with Maria, ruining her in the eyes of society and getting away nearly scot-free.
No, Fanny Price was just scared of sex.
Thank God for Freudian psychology, or we might be compelled to, you know, try to understand the nuances of a character that is widely different from the accepted personality of today's world.