You may be worried about "Pyometra" , that is a very severe infection. I do not have any experience with it, but the symptoms are smelly discharge, fever , etc... you can check it out on this link:
Pyometra - Wikipedia, the free encyclopedia
Hopefully it is not what your girl has.
My females get spayed at 5 and i never saw discharge like you are describing .
Good luck
XOXO