She would be your niece. You're her aunt by marriage !
Your sister's daughter is your niece and you are her aunt (if you are a woman) or her uncle (if you are a man).
She is your cousin
Cleopatra had two husbands. They were both Ptolemy and they were both her brothers.
Your daughter's step-sister would be your step-daughter.
Your aunt's daughter is your first cousin.
neice
Grandaughter.
Neice
Niece
daughter-in-law
step brothers
The name of Peter and Lois Griffin's daughter is Meg and she is the oldest child. Her brothers are Chris and Stewie.