Your girl needs to see a vet ASAP.
She may have a life threatening uterine infection called Pyometra:
It could also be a UTI but in any event she needs immediate vet care.
UTI's must be treated with an effective broad spectrum antibiotic like Clavamox or clidimycin and for a long enough duration so all bacteria is eradicated. If not, they will refluorish, stronger and more resistant and reinfect him. In addition, the bacteria can become tolerant of the same anibiotic so the medication should be varied for best results.
Please let me know how she is doing. I will be here late.
Sincerest best wishes,
Yes there could be a mucus plug a few days befor delivery but it should not have any fowl odor.
Are her nipples pink? is there any milk?
She could have an infection, dead kitten or detached placenta:
Sometimes cats can develop uterine infection, the symptoms are:
pain, fever, odorous discharge, in appetite and pale gums.
Keep a sharp eye on her. A cats appetite is the best barometer of her health.If she wont eat she could be sick or ready to deliver.
Her temp will be 100 or below if she is and 103 or higher if she is sick.
Best wishes for her,