Skin... something

Hey everyone! Been a while since I asked a question but this one's important. I have an appt. with the vet for tomorrow but was curious if anyone could possibly give me a head's up as to what could be wrong. My cat Angel is showing signs of hair thinning and has developed some sort of scabs on her neck, and a few on her head... At first I thought maybe her and the dog had just played a little rougher than usual but they didn't actually seems to be wounds, just scabs. They don't seem to be getting worse, but they haven't healed and my bf noticed her thinning coat just the other day... Her diet hasn't changed at all in over a year and the only thing I've been able to come up with is a possible allergy to a different litter I'm using, but why would that make scabs on her neck? I also don't really think it's fleas because I've checked her regularly since noticing the scabs and haven't found a single flea or... she also doesn't seem overly itchy or to be in any pain... and she hasn't had on a collar since winter started, even she has no desire to go outside when it's cold! I wanted to put a couple pictures up for possible clarity so please, if anyone can let me know what kind of vet bill this is going to lead to it'd be a great help. I just want to help my baby!

Could be a bacterial skin infection...not the same species but it looks just like the skin infection my rattie had last summer.

Sending healing vibes to Angel.