These conditions weren't anything outrageous. With Savine's profits, Fest's debts would be paid to the Sovereignty in eight months, and all the other advisors would have something to be happy about as well.
As for the second condition, it wasn't really a condition. It was common sense. But since Savine was going out of her way to express it, people had to take it somewhat seriously.
Of course, the biggest thing that Savine was getting out of this was a marriage with the Prince.
She would become a member of the royal family and though her authority won't be as big as one, the title was enough for her to do almost anything she wanted.
And in a way, it wasn't like she was the only one getting anything out of this. Since she now has all this authority, she has no excuse to not be able to dedicate herself to the Sovereignty. Moreover, working for the country was in the job description of being a princess.