Marion's signs could have a few causes.
We do know that the Kennel Cough vaccine can cause a mild illness in some dogs in the days after vaccination. However, they should remain relatively well, so there may be more going on here.
As her signs are getting worse and she has a discharge, I'd wonder about a bacterial infection, nasal polyp, allergic rhinitis or foreign body within the nose (such as a grass awn).
Frenchies are more prone to respiratory disease, and less able to cope with it, due to the shape of their face.
She sounds stable for now so we should be okay keeping an eye over night. However, I'd advise a vet visit in the morning.
They will examine her and listen to her heart and lungs, as well as assessing her hydration and temperature.
It may be that she requires some antibiotics and/or anti inflammatories.
At home, ensure she continues to eat and drink and keep the air well ventilated and free of dust, smoke and cooking fumes.
Clean away any discharge with a moist tissue or cotton wool when needed.