Although there are questions that de Lima needs to answer, including on the Napoles/Pork Barrel scandal, Arroyo and about the Mindanao Massacre, on the balance of probabilities I'd say she's likely to be innocent of any drugs-related offences for which she has just been arrested.
Apparently she was out the first time the CIDG and armed SWAT teams descended. They had to push a 'Sorry you were out when we called' card through her letterbox.