That is not normal.
Has she been running, and playing.
I have heard of spay hernias, I just haven't seen one in person.
If she has torn the stitches in adominal wall, mine would be at the ER vet. I suggest you call your vet immediately, and see what he / she says.
If you have no way of getting a hold of your vet over a weekend. I would take her to the ER, and let them check her out.
Not all those who wander are lost.
Life is just a leap of faith.
Spread your arms and hold your breath and always trust your cape.
Two things define you. Your patience when you have nothing, and your attitude when you have everything.