As you might imagine, proving that someone was driving a particular car at a particular time and that they were drunk whilst doing so requires a bit more than seeing that the keys were left in the ignition. It might go like this:
If they were left, who left them there?
Did that person drive the vehicle or did they just switch on the ignition to check the fuel level?
If they did drive, and you can prove who it was, were they drunk at the time or did they have an enormous shot of Brandy when they got in to recover from the shock of an accident? (�Smelling alcohol on her breath� � even if it was accepted - is not sufficient to prove that she was over the limit)
Were the breathalyser procedures at the roadside and the evidential specimen procedures at the police station properly followed?
And so on.
There are 101 reasons why this person may have pleaded not guilty. It is no use worrying about it until the trial and even then, as far as I can see, you can have no evidence to provide that proves her guilt in any of these matters.
Finally, none of the matters you mention are linked. That is, a conviction of one offence does not lead to an automatic conviction of any of the others. They will each separately have to be either accepted or proved.