Possible Clues:

• "Believe" pop diva
• Dear, in a billet-doux
• Singer with the 1999 #1 hit 'Believe'
• Fr. for dear; US singer
• US singer; dear (Fr.)
• One-named singer and Oscar winner
• She topped the UK charts at the age of fifty two
• Word in a billet-doux
• 'Mermaids' actress
• Alicia in 'Clueless'