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This may just be a mole. That is an area of increased pigmentation on the skin. They are typically benign and you can ignore them.
If she were older, I'd want to biopsy it to make sure it's not melanoma. These can look similar. To be on the safe side, it wouldn't hurt to have it removed and biopsied. Most vets will just make a note of it and monitor it year to year. If it all of the sudden starts growing or changing, then it's removed and biopsied at that time.
I hope this helps, let me know if you have any other questions.