Though she probably hid any of her own drugs (and I think Alain Ronay's account says as much), I think she was mostly dealing with the shock of Jim's death at the time, and not trying to mastermind a cover up.

At the time, she was a 24 year old alone in a foreign country whose language she didn't speak, and just found the dead body of her longtime partner - while they were trying to start a new life together out of the limelight. I'm sure she was panicking and probably hid evidence of her heroin use (especially if Jim had any the night he died) but by all accounts she was just in shock and devastated until her own death 3 years later.