Hard/crusty nose with drainage on one side

Hello vets! I’m curious if anyone has theories. 8 y/o pit mix. We noticed the side of her nose starting to get kind of hard around around 6/27, along with nasal drainage on that side only. It has slowly looked worse (crusty?) each day. For the most part she is behaving as normal, but she has shown reluctance to eat breakfast, and sometimes skips it altogether. She always eats her dinner though.

Hello - I'm sorry to see this and please do take it seriously.  Discharge from one side of the nose (i.e. one nostril) only can imply a blockage further back in the other, for example a cancer.  However I have a second theory, because I wonder if the discharge is coming from the skin rather than down the nose here, which makes me wonder about skin damage to the discharging side e.g. fungal disease, skin cancer or auto-immune disease (not sure why the last would only be one side, though).  Either way, this certainly has the potential to be very serious, depending what is causing it, so please do go and see your vet.