Talking to her about going back to the gym might seem like a hint to her that you are not happy about the way she looks and make her pull away. Try more subtle things like asking her to go for a walk with you and S or you alone and make it a habit. The plus to this is that you are also spending time together and she won't fel that you are unhjappy with her looks.
JAK
You don't get to choose how you're going to die. Or when, you can only decide how you're going to live now. ~Joan Baez
