“My husband wondered last night if she has taken testosterone. (We don’t believe she’s actually a biological man.)”
When it comes to high-ranking female athletes, one often sees very flat chested women. The pictures other commenters have posted on this thread show that Greiner has almost no breasts. That could easily be due to her taking testosterone. Of course, that leads one to ask whether the WNBA has any rules against taking testosterone. I don’t know what the answer to that question is.
Retardation of secondary sex characteristics is sometimes also caused by excessive exercise in developing years. This used to happen a lot to serious ballet students/dancers.