Well said LauraMarie! (:D) Perhaps this is part of what makes Fanny so miserable after Edmund decides he will act after standing against it on principle with Tom and Maria. Although he speaks of “restraining the publicity of the business, of limiting the exhibition, of concentrating our folly” (15) he is far warmer on the subject of gallantry in the service of Miss Crawford:

Consider what it would be to act Amelia with a stranger. She has a right to be felt for, because she evidently feels for herself. I heard enough of what she said to you last night to understand her unwillingness to be acting with a stranger; and as she probably engaged in the part with different expectations—perhaps without considering the subject enough to know what was likely to be— it would be ungenerous, it would be really wrong to expose her to it. Her feelings ought to be respected.” (15)

Edmund has chosen pleasure over principle and Fanny is sorrier to see him so unsteady than she is for Miss Crawford’s predicament. I can’t see that Mary has much of a predicament. She only developed scruples after she found Edmund could not be charmed into acting. Fanny is astonished and distressed because she sees Edmund following Mary into impropriety as Maria did Henry at Sotherton:

Was he not deceiving himself? Was he not wrong? Alas! it was all Miss Crawford’s doing. She had seen her influence in every speech, and was miserable. The doubts and alarms as to her own conduct… were become of little consequence now. This deeper anxiety swallowed them up. Things should take their course; she cared not how it ended. Her cousins might attack, but could hardly tease her. She was beyond their reach; and if at last obliged to yield—no matter—it was all misery now. (15)