I'm fairly certain they went "she's not dressing sexy enough" (Claudia was sort of... businessy/frumpy, in a way that Jenny definitely is NOT).

Oh, agreed. Just the way they introduced Jenny--didn't they start down at her stilleto heels and work the camera slowly upward?--indicates what they were aiming for with changing her character. (SO. ANNOYED. I really did like Claudia; she was probably the most human of the characters on the show.)