people are often so concerned about reducing calories that they forget that you NEED a certain amount if only to be a carrier for the micro-nutrients a body needs. They end up under-eating and overexercising and find themselves in a cycle of messed up metabolism in conjunction with injury. I would suggest that you talk to your client also about body fat and make that part of the goal. You mention only aerobic activity. Some strength training would be a great addition.
I wish you and her best of success.