I sure don't know much about the physical stuff, but I agree with what Jill is saying.
Maybe what's important for now is to structure her sessions so that your client feels like what she is doing is actually doable for the long haul. She may see her road to fitness and weight loss as an enormous hill to climb. If she sees it as too high to ever reach the top, she may get discouraged too early in the game. Keep it interesting and challenging and most of all...make it fun, ('cause you ARE fun to be around!

) Could you do the work with her so she feels like she has a workout buddy, play some upbeat music, etc.?