“Perhaps,” said Tom, “Fanny may be more disposed to oblige us now. Perhaps you [Edmund] may persuade her.”

“No, she is quite determined. She certainly will not act.”
“Oh! very well.”
…Fanny felt herself again in danger, and her indifference to the danger was beginning to fail her already. (17)

Fanny was dispirited by Edmund’s unsteadiness in deciding to act and felt if she were “at last obliged to yield” (16) it could not make her more miserable than she was already. Yet when Tom asks Edmund to persuade Fanny to act (above) and though it comes to nothing Fanny felt herself in danger again and that her is indifference already failing. Fanny still feels it wrong to act and she could not do it without feeling herself to be very wrong. Fanny does read lines with Mary and Mr. Rushmore and perhaps this is a reason why Edmund joins the others in asking Fanny to just read the part of cottager’s wife when Mrs. Grant misses rehearsal:

After a pause of perplexity, some eyes began to be turned towards Fanny, and a voice or two to say, “If Miss Price would be so good as to read the part.” She was immediately surrounded by supplications; everybody asked it; even Edmund said, “Do, Fanny, if it is not very disagreeable to you.”

But Fanny still hung back. She could not endure the idea of it. Why was not Miss Crawford to be applied to as well? Or why had not she rather gone to her own room, as she had felt to be safest, instead of attending the rehearsal at all? She had known it would irritate and distress her; she had known it her duty to keep away. She was properly punished. (18)