tooticky, I am rubbish at 'punishments' and my ds is much younger so I can't suggest much, I just wanted to echo the thought behind Alexmummy's post - was it clear to your DS that his sister had a consequence for hurting him?
I totally understand that you say he hurts her all the time, etc; but my DH (who has worked many years in a boy's senior school and knows what makes boys tick, I reckon) says that fairness and justice becomes INCREDIBLY important to boys. People being seen to 'get away' with things, or punishments not applied equally to all, make the boys go MAD my DH says!
I just wonder if your DS' actions were to do with this; doubtless he doesn't have it in him to think "Oh, well my sis did hurt me but I've hurt her loads in the past so maybe I'll let it go"!! Kids just deal with the here and now, and live in the moment....
Going on my DH's observations your DS would need your house rules/punishments to be crystal clear and very consistently applied.
Personally, missing out the punishment aspect of it cos I am crap at that, I would definitely have a chat with him about how upset his sis is that he has ruined the things she made, and that it would be really really nice of him to make her a little something himself. I wouldn't 'Make' him do it or stand over him while he did it, just have the chat and ask him what he thinks she would like from him; and encourage him to do it rather than make it a forced thing. It would be lovely for their emotional connection with eachother if he does it himself.