Outdoor cat eye goobers

Hello. I am caring for an outdoor/stray cat. We have done TNR so she is spayed and has basic vaccines. She does get into scraps with the local wildlife sometimes. We do our best to take care of her, but she definitely doesn't care for people or the vet. She tolerates me somewhat when I feed her.

As long as she's been around (a few months now) she has had a goobery eye. Today it looks especially bad. The crusties are usually black but today look dark red colored. Is there a illness in particular that this could indicate? Anything OTC that I could try to put on it?

Our shelters are unusually full and she seems happy to be her feral self, just trying to do the best by her without spending a fortune on vet bills.

Thanks in advance for any help or advice!