What is this Aussie pink snout problem (photo)?

I'm hoping someone might be able to tell me what my Aussie's pink and hairless snout problem might be. (see photo)

It's slowly going up towards her eyes. It doesn't seem to bother her.

She gets Purina One Chicken and Rice food, Interceptor Plus for worms and Bravecto for fleas and ticks (just gave her the good-for-3-months Bravecto pill a couple of days ago).

I got her as a stray 13 months ago. Vet says she's 5-6 years old.

I'm in Tennessee.

Thanks!