To be honest, you need to ask your girlfriend what it is that is bothering her. Is it the fact you'll be in prison, or is it perhaps that she doesn't want to be with someone who has obviously commited what some would say is a 'serious' crime.
I know that my boyfriend would be very unlikely to do something like this, but whether i would stick by him would depend on the circumstances for example what exactly happened, was it in self defence etc? However, consider for a moment that you already have a suspended sentence, you could have taken this as a warning and if it was me, i would not be able to be with someone who has done this once already and learned no lessons.
Also consider the idea of you being in prison - no one knows yet how long yoru sentence will be for. Put yourself in her place, could you really handle being alone that long and the idea of her being in prison. Say for instance, you get a 5 year sentence, 5 years is a lot of your life to waste waiting for someone, especially if you're not sure you're the one.
if she isn't prepared to wait for you, maybe she isn't Miss right and on your release from Prison, she may be wating for you and you can make a new start and perhaps have learned something on the way.