She may have missed you, and was fretting. Strange though too notice weight loss in just a week. Well enough to notice like that. But if you've had her checked that's what my gut would tell me.
Also maybe they were feeding her more treats than you, I mean they are so cute, ;)and she didn't eat as much of her feed.
Try some oatmeal, large flaked, that seems to put a few grams on them. Cut back her treats to make sure she is eating enough pellets.