I agree, any confrontation with your sister will fall on deaf ears or else possibly fuel aggression towards you.
Your neice is in need of support, let your sister face the consequences of her behaviour in full. Have you and your neice begun to attempt detachment and keeping to your 'own side of the street' (as i think the saying goes); i.e. the choices are always infront of you both to either participate in the madness or, as hurtful as it can be to begin with, walk away and leave her to it. She doesn't have to pick her up any where if this is a cause of pain and frustration, and the phone can be hung up..
It is difficult but sometimes the first step to take is to protect yourself from the continual hurt and suffering.
Lily xxxxxxxxxxxxxxxxxxxx