Hi. Very hard to tell without seeing it. How old is she and is she spay?
What you need to do is try to clean it and see if anything comes off. I would use a little warm water and a mild soap or some oil, like cooking or olive oil.
Get some Q-tips, lay her Diwn and "gently" moisten the area, let it sit for a bit then gently see if you can remove any residue with the Q-tip. If so, finish cleaning it, dry and keep an eye on it.
The black color concerns me a bit and if it won't clean off, best to have your Vet take a look at it, really, any suspicious lumps should be checked if it is in question.
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