Any tips about training a client who had gastric bypass surgery 5 months ago & eats 600-800 calories/day?

She had gastric bypass surgery in January 2013 and lost about 70 lbs. She currently eats only 600-800 calories a day, primarily protein. She is active on her own and always has been, generally working out 3-4 times a week (lately closer to 2) in a variety of ways: swimming and circuit training are her favorites. She still has another 50-70 lbs to lose and wants to make sure she's doing what she can to make her body strong and build muscle. She wants to train with me only 1 day a week initially. Any tips or recommendations for me? My main concern is the caloric intake since I have never trained anyone who had this surgery before and I know her stomach is smaller and can only hold so much. The calorie amount is just really, really low for someone who is going to be working out a few days/week in my opinion, although it sounds as if it has been working for her thus far. Thanks!