Robyn has no ovaries, but her external genitals are those of a normal female. As she grows up, her body remains short, she does not develop a mature feminine physique, and she does not menstruate. Robyn most likely has:

Robyn most likely has Turner Syndrome.

Explanation:

Turner Syndrome is a genetic disorder, which affects a female's development. It is the consequence of an alteration in an X chromosome in which it could either be incomplete or missing.

It affects the female's physical development, since it primarily inhibits sexual maturation. It is generally difficult to diagnose until puberty, since its affections can be seen during this stage.

Robyn's body remains short and she does not develop a mature feminine physique and she doesn't menstruate. These are Turner Syndrome symptoms and she most likely has this disorder.