Thanks for posting your query on health care magic.
Absence of menstruation
till the age of 26 is a serious problem.
She needs to be evaluated in detail for presence or absence of uterus
and outflow tract.
Also genetic abnormality in terms of turners syndrome can present with absence of menstruation.
I suggest her to visit a Gynecologist at an earliest and get examined. Karyotyping is also necessary.
Hope this helps.