Yes, from reports she is the most influential advisor to Obozo.
And she is fluent in Farsi, she was born and grew up in Iran.
It has also been said that Obozo is fluent in Farsi too.
You can find that on the Internet. But Obama has enough trouble with English. I don't doubt that Jarrett understood and could speak Farsi at one point, but if you lived in a country for the first 5 years of your life, half a century ago, how much would you really retain?