Crusty patch in new kitten head

Hello everyone!

Me and my gf just got a rescue kitten 3 days ago and we noticed she had a dry bald spot on her head

Feels very dry like kind of a crust

We're thinking might have been some injury or something?

We also have another cat a 1 year old girl

She had similar reaction in her neck when we got her but it wasn't dry , that was because she was having allergic reaction to her food and we got that sorted out

Any help is welcome

Thanks