Possible Clues:

• R&B singer of "Case of the Ex"
• 'Case of the Ex' singer, 2000
• "Case of the Ex" R&Ber
• One-named "Fear of Flying" singer
• R&B singer whose name anagrams to "Amy"
• One-named RandB singer
• Single-named RandB singer
• One of four singers on 2001's "Lady Marmalade"
• One-named R&B vocalist
• Grammy winner for 2001's 'Lady Marmalade'