Oh my stars! They should not have covered that incision for sure. Poor little dog looks so sore. I hope she is doing WAY better now.
We had our girl spayed four days ago today. She was done one morning, home the next morning. They never covered her incision and its approx. an inch and half long. They sent her home with metacam for pain for five days. I hope you will seriously consider getting another vet, but don't beat yourself up. YOU did nothing wrong. The vet did. It is his/her responsibility to care for you dog. I personally think they should have repaired the hernia also while she was under. Why subject them to two surgeries and anesthetics when it could have been done all at once. I think the muscle excuse is a load of hoopla..(JMHO)
If you click on this link and click the picture you should be able to view larger..
Roxy incision four days after spay surgery.jpg - Windows Live