Hi, saffron, I'm a vet so might be able to help a little. I usually say that they can be walked but ON THE LEAD, starting with shorter walks and building up.
gentle walking will do stitches far less harm than leaping around the house, so no chasing frisbees etc, but IMO better to get her out the house and getting gentle exercise than going mad in the house! On the plus side, if she is behaving like this, it shows she is feeling very little in the way of pain, which still amazes me, given what major surgery it seems to be in humans!
Is she on any pain relief? I am a bit of a mean old meany, and tend to give lots of painrelief peri-operatively, then only follow it up if necessary. It sounds harsh, but in animals if they overdo it and feel a twinge of pain, their body tells them to be careful, but if they are loaded up on pain killers they might not get that message (hope that doesn't mean I would leave an animal in pain- far from it, but I try to give it where it's needed only, iyswim!)
Don't feel sad about neutering her. I watch the guilt on the faces of clients whose elderly bitches develop pyometra (a common condition in unspayed bitches) and need an emergency hysterectomy at a time when they are old and very sick. Some of those guys don't even make it to the operating table 
By neutering you have also reduced her chances of developing malignant mammary cancer by about 99%, as well as preventing her from ovarian and uterine cancer! As you can see, she is not overly upset- you have done a good thing for her in terms of her future health, so don't fret!