Only if you ignore the law which requires you to identify the driver and/or take the risk of a charge of attempting to pervert the course of justice, both of which generally carry a much larger sentence than the speeding. If she was the only person likely to have been driving the car at the time, as is likely to be the case from the info given, then they're likely to be able to make a pretty good case for the latter if she decides to mess around.
Fair point, but if there is a case that one of several drivers may have been driving the car at the time, but you are uncertain as to who it was, provide each name and address of the likely drivers, then surely this is not perverting the course of justice?
And if it is, how come I know people that have managed to do this (recently) and got away with it?
And yes, attempting to pervert the course of justice would just be totally bloody stupid, I should add!