Question

Como se diz she is my sister na forma interrogativa e negativa

Answer 1

is she my sister?
she is not my sister or she isn't my sister

Answer 2

Negativa: She is not my sister ou então pode ser na forma contraída: She isn't my sister.
Interrogativa: Is she my sister? 
Na forma interrogativa, basta você inverter o to be. 
A forma afirmativa é
I am
You are
He is
She is
It is
We are
They are
A forma interrogativa, basta inverter o to be para frente, 
Am I?
Are you?
Is he?
Is She?
Is It?
Are we?
Are they?