I would think the medical examiner would have the answers to these questions. They run all types of toxicology test which tell them how much of a substance was in the deceased’ blood.They also know the amounts of a substance it would take to stop a heart.
It depends how much Valium she took. if it was alot and she is drinking, she needs to to quit drinking and possibly go to the Emergency room to see how much is in her system. Drugs and booze never mix.