It would depend on what country he was in.
And what state. And whether there is plea-bargaining, any circumstances, and what the social context is - courts often 'send messages' through sentencing, and prosecutors can agitate for sentencing for political reasons; sentencing can be very political.
In a place like Australia where I live I think that if a custodial sentence were imposed at all for negligent driving occasioning death, no prior convictions, no public outrage... I think that the chances are that it would be something like 1-3 years, with chance of parole halfway through. In some circumstances though, it could be loss of license and good behaviour bond with no custodial sentence - or maybe home detention. If it were something more severe (like driving a getaway car for an armed robbery, and the girl had no previous involvement), then it could be around 5 years, plus whatever they get for the other crime.
