The hardness could be attributed to the internal sutures. All of our females, after being spayed, had the exact same thing. A little puffy, and a little hard, along the incision. The vet has always said, that besides the stitches on the outside (the ones that you can see), there are also stitches on the inside, and that could be the reason for the hardness.
As long as she's acting fine, and you keep up the antibiotics, you should be in good shape. Maybe some topical ointment to stop the puffiness, is all I can add to this. Triple-antibiotic is available OTC from Walgreens/CVS/etc, and works very well for incisions. I will warn, however, that if the incision is open, to call your vet immediately and take your dog in to see him/her. Open wounds on a dog are never a good thing.
The same thing happened when I got both my little girls fixed. It took about 6 months for the hardness to go away and about a month or so for the redness to disappear. They are both Happy and Healthy now with no sign's of babies to come! :)
Hope your Dog gets to feeling better soon! Just make sure she doesn't constantly lick the site or it will take alot longer to get rid of the red spot and heal up.
It sounds like she feels ok. Usually when a dog feels pain it won't eat, and is lethargic.
Does the scar look normal? Or is it oozing at all, or very red and inflamed? How bad is the swelling? Usually if there was infection at the incision site, there would be inflammation as well. And if there were some infection internally, there would be a marked change in her, as she would probably have pain and fever.
It's hard for me to know and give the right advice from a distance, as I can't see the scar. And I would always say it's best to ask the vet who did the surgery on her if you have any questions post-surgery. Or if you are really unsure, take her in to be examined.
But I can say that a scar does take some time to completely heal and swelling to go away. I had abdominal surgery once and the scar felt harder than the surrounding skin. Also there is still a numbness for about 1/2 " on both sides of that scar even years later.