'I will not...
...sir."
I love that part in the movie! I also find it funny that she gets such a long lecture from her uncle for "talking back" at him very mildly. Back then, I am sure that this was considered as bad as kids swearing at their parents today. However, his reaction was so extreme not just because of the money involved in the union but because he finds her ungrateful. His own daughters are already priveledged and are even more greedy by wanting more money through marriage; Fanny refuses her one opportunity of wealth. I think he feels angry that she rejected "his" help.
I love her delivery of the line: cold yet restrained.