13-month-old with low red blood cell count?

At my daughter's routine 12-month-old checkup, the results of her blood work came back with a low hemoglobin count (around 8.2). We were referred to a pediatric hematologist who performed further blood work. Once again, her hemoglobin came back at 8.2 but absolutely everything else (including iron, b vitamins, folate, white blood cells, etc) came back normal. This took place about 5 days after the initial blood test. Her doctor suspects a condition called diamond blackfan anemia, but I am personally skeptical because it is so rare. My daughter is showing zero signs of being anemic or ill...she is extremely active, never tired, and looks very healthy. She has had a cold on and off for the last month or so, and I'm wondering if her body's suppression of the virus(es) could be contributing to her low red blood cell count. Also, they want to perform a bone marrow biopsy, which scares me half to death. Does anyone have any experience with a bone marrow biopsy on such a small child?