
Green discharge is seen when a placenta separates from the uterine wall ( hence a big worry if seen before any pups have been delivered) so what you felt was probably a retained placenta which would not show up on Xray as it doesn't contain any bones, did the vet give her an injection to empty the uterus of anything left behind.
I hope you got some antibiotics to stave off any infection, if not then keep a very close eye on her, first signs of abnormal smell/discharge she needs to get back to the vets pronto.
My girls won't eat normal dog food after whelping so I add broth, cottage cheese, goats milk or yoghurt to the kibble and it goes down well
Hope all settles down now.