Line?

Yes, that line was an invention added to this adaptation and the '99 film. No one had any idea how Fanny felt about Edmund, least of all Edmund himself. Sir Thomas was happy they got together, Lady Bertram less so because she was selfish and wasn't keen on the idea of Fanny leaving home. She eventually became reconciled to the idea though.

... Edmund did cease to care about Miss Crawford, and became as anxious to marry Fanny as Fanny herself could desire.

With such a regard for her, indeed, as his had long been, a regard founded on the most endearing claims of innocence and helplessness, and completed by every recommendation of growing worth, what could be more natural than the change? Loving, guiding, protecting her, as he had been doing ever since her being ten years old, her mind in so great a degree formed by his care, and her comfort depending on his kindness, an object to him of such close and peculiar interest, dearer by all his own importance with her than any one else at Mansfield, what was there now to add, but that he should learn to prefer soft light eyes to sparkling dark ones. And being always with her, and always talking confidentially, and his feelings exactly in that favourable state which a recent disappointment gives, those soft light eyes could not be very long in obtaining the pre–eminence.

Having once set out, and felt that he had done so on this road to happiness, there was nothing on the side of prudence to stop him or make his progress slow; no doubts of her deserving, no fears of opposition of taste, no need of drawing new hopes of happiness from dissimilarity of temper. Her mind, disposition, opinions, and habits wanted no half–concealment, no self–deception on the present, no reliance on future improvement. Even in the midst of his late infatuation, he had acknowledged Fanny’s mental superiority. What must be his sense of it now, therefore? She was of course only too good for him; but as nobody minds having what is too good for them, he was very steadily earnest in the pursuit of the blessing, and it was not possible that encouragement from her should be long wanting. Timid, anxious, doubting as she was, it was still impossible that such tenderness as hers should not, at times, hold out the strongest hope of success, though it remained for a later period to tell him the whole delightful and astonishing truth. His happiness in knowing himself to have been so long the beloved of such a heart, must have been great enough to warrant any strength of language in which he could clothe it to her or to himself; it must have been a delightful happiness. But there was happiness elsewhere which no description can reach. Let no one presume to give the feelings of a young woman on receiving the assurance of that affection of which she has scarcely allowed herself to entertain a hope.

Their own inclinations ascertained, there were no difficulties behind, no drawback of poverty or parent. It was a match which Sir Thomas’s wishes had even forestalled. Sick of ambitious and mercenary connexions, prizing more and more the sterling good of principle and temper, and chiefly anxious to bind by the strongest securities all that remained to him of domestic felicity, he had pondered with genuine satisfaction on the more than possibility of the two young friends finding their natural consolation in each other for all that had occurred of disappointment to either; and the joyful consent which met Edmund’s application, the high sense of having realised a great acquisition in the promise of Fanny for a daughter, formed just such a contrast with his early opinion on the subject when the poor little girl’s coming had been first agitated, as time is for ever producing between the plans and decisions of mortals, for their own instruction, and their neighbours’ entertainment.

Fanny was indeed the daughter that he wanted. His charitable kindness had been rearing a prime comfort for himself. His liberality had a rich repayment, and the general goodness of his intentions by her deserved it. He might have made her childhood happier; but it had been an error of judgment only which had given him the appearance of harshness, and deprived him of her early love; and now, on really knowing each other, their mutual attachment became very strong. After settling her at Thornton Lacey with every kind attention to her comfort, the object of almost every day was to see her there, or to get her away from it.

Selfishly dear as she had long been to Lady Bertram, she could not be parted with willingly by her. No happiness of son or niece could make her wish the marriage. But it was possible to part with her, because Susan remained to supply her place.

The people have appointed me. I am their leader. I must follow them.