Aslam

Praise be to Allah.It is permitted, because she is not one of the mahrams mentioned in the aayah

(interpretation of the meaning):

“Forbidden

to you (for marriage) are: your mothers, your daughters, your sisters,

your father’s sisters, your mother’s sisters, your brother’s daughters,

your sister’s daughters, your foster mothers who gave

you suck, your foster milk suckling sisters…”

[al-Nisaa’

4:23]

What is

listed among these mahrams is “your

sister’s daughters”, and the girl – in this case – is not the daughter

of your sister. So there is no reason for this marriage to be haraam,

either on the grounds of blood, breastfeeding (radaa’ah) or being related

by marriage. And Allaah knows best.