Breast buds and body hair in a 20 month old baby who is breastfeeding. I think that your pediatrician is very comfortable with the normal variants. Firstly each finding is separately influenced. The breast buds could just be normal from "mommy's hormones" and yes if you are nursing this is common, if it is sudden and worsening there can be an influence of estrogen perhaps from a simple cyst on her ovary-actually the more common cause. So in regards to the breast development, monitor, at her 24 month visit if it is still there discuss it again with your pediatrician, tests to get include thyroid, LH, fsh, estradiol and even a pelvic ultrasound (transabdominal) by a good pediatric radiologist, then monitor.
As far as the hair, if it is not curly and it appears like body hair your hunch is right, you describe that she is part african american, so yes, her body hair on her back and again in her private area more than likely are hypertrichosis(extra body hair)
But a visit to the endo will answer both questions, You are a good mom, don't have to have a bunch of kids to know better, I like your comfort with this as this is what I would tell you as well in my office if you came for consultation-let the endo check her out, it will settle everyone's mind then you can monitor her all you need and know you already been there done that!
Good signs, no rapid growth, no change in breast(worsening) and no realy pubic hair.
Good luck
I meant to write back earlier i wanted to thank you for your time and your feedback