what is this new brown spot on her nose

My cat seems to suddenly have got this brown spot on her nose, I’ve attached one pic of how it looks now and two pictures of how her nose looked before. Should I be worried, what could it be? She has a vet appt in about a month, should I take her earlier instead? She has had skin cancer on her ear and that’s why she only has one left but I was told it was fully removed and her lymph nodes are not inflamed, but she also has allergies and gets little scabs & build ups of skin around her head & back.