Disagree. Definition of a useful idiot is this: “suggesting that the person thinks they are fighting for a cause without fully comprehending the consequences of their actions, and who does not realize they are being manipulated”

Jill Stein may be aware that she’s been useful to Putin, but that doesn’t contradict the above definition and she can still qualify for the “useful idiot” label. The main thing here is that she’s not a Russian asset - she’s being manipulated perhaps but not under Putin’s Russia’s direct control.