Oscar knows that Sasha is a great source of information, and he's perfectly happy using her as an anonymous source, but Oscar is frustrated by the fact that he usually has to "pay" for the information, instead of Sasha offering the information because she believes in the principles of government transparency.
So, she probably knows more than she ever tells Oscar, but occasionally he'll be able to broker a deal with her such as an exchange of information, or Oscar keeping some other piece of news out of the press, because that's a favor that Sasha can offer to someone else. And just occasionally, Sasha telling Oscar some piece of information that results in an informative article works out well for both of them.