I don't know why she even has stitches.
They can do it differently now so that there aren't any stitches there to bother them. That's how my Vet did Sassy's spay.
Of course, she has a stitch in each leg from her dew claw removal which she tries to lick incessantly, but none on the outside from her spaying.
Hope she feels better soon. I know just how it feels when they are crying like that and you can't do anything to help them. Poor you. My heart goes out to you.