I have a stepdaughter who is well on her way to being plus-sized. She is 12, and weighs 40 lbs more than I do. What can I do to encourage and support her? I am very careful not to make weight/appearance comments (I limit them to "you have beautiful hair" or "I love your gorgeous eyes") and we emphasize the importance of cooking and eating healthy foods; not from a skinny standpoint, but from a healthy body standpoint. We also try to do fun active things with her, like hiking and rock-climbing.
She is very impressionable, and I do NOT want to contribute to her having image issues. While I would like to help her lose weight strictly for health reasons, (and she does want to) I have very little idea what is acceptable to say or do.
It sounds to me like you are being very respectful of her feelings. You definitely don't want to call attention to her weight but if she opens it up for discussion you can ask her what she would to accomplish and if she would like some help. If she says yes you could recommend a daily walking schedule (something you both can do together after school) even if it is only 20 minutes. The other thing you can do is make an appointment to a dietitian so she can hear from a respected health professional the basics of eating. Going together gives both of you an opportunity to ask the dietitian questions. If she doesn't already you may also suggest journaling about her feelings as often times, feelings play a role in over eating. Her privacy must be respected in this manner. And if you have a fireplace you may even suggest she burns the feelings afterword so she feel more comfortable about getting them down and out while having them unread.
It already seems you have a grasp on not pushing the issue. If you and your husband are setting a good example she's sure to appreciate it.
It's also important to remember that it is possible for her to be slightly overweight, active and healthy. And it's more important to judge her health by exams like blood pressure, blood work and activity rather than a BMI which is often skewed for many people.