There is a sub culture that use the police for their own petty acts of revenge in just such instances as this. This seems a simple enough fit up to me if you wanted to orchestrate it.
Unfortunatly for your friend I think it's highly likely that she will be found guilty.
Her best defence is to discredit the witness'. Have there been any instances of bad feeling between the accused and thepeople acting as witnesses against her. Have they reported her to the Police, social services, council, dss, RSPCA wrongly before etc. If they have, dig away at that, it shows that they have a grudge and are lying. the court might view that if they have lied once they will do so again and it may work in your friend's favour.
It's very easy to dismantle someone's entire life simply by falsely reporting them to the above agencies. Before you know it they have problems falling down on them like rain and unfortunatly it's very hard to prevent so long as the perpetrators have their stories straight. If they've done this, tell her to watch out for the rest, but her best bet is to prove a grudge and a lie from the witnesses re the drink driving.