Simplify the following text for a Grade 9 native English-speaking person.
Original: With Decca 's Milt Gabler as her manager , she began working regularly for the jazz impresario Norman Granz , and appeared regularly in his Jazz at the Philharmonic ( JATP ) concerts .
Simplified: Decca 's Milt Gabler became her manager and she began working often for the jazz producer Norman Granz . She often sang in his Jazz at the Philharmonic concerts .