This is a common problem for a lot of women. While we can try to reduce cellulite through diet and exercise, some cases are caused by hormones and genetics. These may be circumstances beyond our control.
However, combining strength moves with high intensity intervals would be a great place to start. Strength training will build muscle and the intense intervals will burn calories. The combination of strength training and intense cardio is great for fat loss.
In addition, your client could try reducing sugar and salt in her diet, and drinking more water to aid in this process.