The character Samar Navabi is Iranian by birth, so what motivated her to sign on with an Israeli intelligence agency?
In the show we learn that she was recruited by Mossad.
From The Blacklist wikia,
Samar Navabi is a Mossad operative who has had past interactions with Raymond Reddington. With the death of Meera Malik, she is assigned by Deputy Director Cooper to the task force as an investigative agent and Mossad liaison.
She is an Iranian-born Baloch, we learn, who was radicalized and, one assumes, recruited by Mossad because of the mistreatment and killing of her parents by the Iranian regime.
further readings > Wikipedia
In the episode "Zal Bin Hassan", Samar's past is revealed and how she witnessed the death of her parents. She joined mossad to find and get her parents' killer to justice.