I am also going to say that that looks like a nipple. But, that being said, it's hard to discern from the photo exactly where the "growth" is on her body. If it's something you've never noticed before and you are concerned, it may be wise to make an appointment to see the vet. Sure, if it is a nipple, you may feel silly. But, I'd prefer feeling silly than potentially missing something important. There are many things that lumps and bumps and growths can be. My opinion is generally "better safe than sorry."
Good luck and please let us know if you do decide to go to the vet. Hopefully, it is just a nipple or harmless growth. I'll keep you in my thoughts!