Possible Clues:

• The "O" of OWN
• The 'O' in O Magazine
• Barack awarded her the Presidential Medal of Freedom
• Talk show host Winfrey
• Host with a book club
• First name in daytime talk
• Dr. Phil's mentor
• The 'O' of O magazine
• Talk show ending in 2011
• Dr. Phil was her frequent guest before getting his own show