I think that you should do a regular spay on your girl. Her complicated c-section must have caused adhesions that can cause complications latter. Opening her up would give the surgeon a chance to check on that.
I have seen pyometra in cases where the uterus was left alone. I've also seen stump pyometra. So the risk is always there.

These pyos after spays are caused by remnants of ovarian tissue that are left behind; if you have a careful and diligent surgeon, post-spay pyos can't happen.