I think there's a lot going on there.
She really doesn't want to it, she doesn't seem to want to be the center of attention. She doesn't think Sir Thomas would like it.
Quoting from ch. 16- It's long but I think it all is to the purpose
But she had more than fears of her own perseverance to remove: she had begun to feel undecided as to what she ought to do; and as she walked round the room her doubts were increasing. Was she right in refusing what was so warmly asked, so strongly wished for—what might be so essential to a scheme on which some of those to whom she owed the greatest complaisance had set their hearts? Was it not ill–nature, selfishness, and a fear of exposing herself? And would Edmund’s judgment, would his persuasion of Sir Thomas’s disapprobation of the whole, be enough to justify her in a determined denial in spite of all the rest? It would be so horrible to her to act that she was inclined to suspect the truth and purity of her own scruples; and as she looked around her, the claims of her cousins to being obliged were strengthened by the sight of present upon present that she had received from them. The table between the windows was covered with work–boxes and netting–boxes which had been given her at different times, principally by Tom; and she grew bewildered as to the amount of the debt which all these kind remembrances produced.
So even though she thinks it's wrong, she doesn't want to act on her own account either. However I think all of the "excessive agitation" is because she's never said NO to anything that has been asked of her.