Ruth told the FBI about Oswald’s letter to the Soviet Embassy. Therefore she was an informant about that, at least.
Yes, , You're right, the FACT that Ruth Paine retrieved Lee's rough draft of the Russian Embassy letter from the waste basket and typed it up to give to FBI agent Hosty is confirmation that she was an informant.
One of the Loony LNer's thinks she was simply a good citizen..... But that's a very shallow and unreasonable view. Ruth Paine intruded into the Oswald's life in early 1963 and had far more than a passing interest in them......