dog lovers help me out

[sniper7]

My little dog Lucy had a small thing on her right arm that I looked at a few weeks ago, didn't seem to be an issue as I thought it was maybe a bite or she got poked by something running around at my dads.
Just got home from a trip and I find this:





I'm planning on taking her to the Vet tomorrow unless you guys have seen this before and know what it is. I'll be researching it tonight as well trying to figure out what is going on.
She is a 4 year old Lhasa Apso.

He skin is dark right there, quite a bit darker than normal. it is almost like a scab but the skin feels about twice as thick or so. nothing came out of it, no puss or anything like that.

thanks guys.