She is not
Slightly tricky question.
Depends upon what you mean by related.
One definition: Connected by common ancestry or sometimes by marriage
But not in the sense of "DEGREES OF KINSHIP BY CIVIL LAW.
Not in terms of immediate family. But as relatives she is related to you
Only if you are living in a soap opera.
She is your sister-in-law's sister. Technically not related but close to it.