|A) Shreya, she who is my best friend, is a singer.||B) Shreya, who is my best friend, is a singer.|
|C) Shreya, is my best friend, who she is a singer.||D) All of the above|
The relative pronoun acts as the subject or object of the relative clause. It replaces words like she, he, him, her, they, them etc.
It is, therefore, wrong to repeat the pronoun in the relative clause.
Hence, the correct sentence is Shreya, who is my best friend, is a singer.