Yes she is.
Yes, she has some Jewish heritage from her father, but as the Jewish linage goes on down the female line, no Sarah is not Jewish.
Naturally, anyone on earth who finds the name attractive is entitled to use it. But yes, it is a popular name in Jewish families, being the name of the original matriarch of the Jewish people, Sarah...
Yes she is a Jew.
Yes, at least when she's working.