A 13 yr old female having normal ovaries but small uterus

A 13 yr old female having normal ovaries but small uterus(55mm×42mm×44mm) with no onset of menses
What can be the cause?
Pls reply

MRKH no uterus and no cervix. Could be imperforate hymen.

MRKH can also manifest with hypoplasia of uterus and vagina. Since the size is mentioned in particular here, it could be the answer.