Please do not follow waterboatman's advice and suggest she loses weight as this will only make her feel worse. I am speaking from experience of being a large woman who is in a similar situation. I am massively insecure about myself and even though I know my husband loves me, I still get worried about him leaving me for a slimmer model. Little gestures work better for me than anything. Him buying me a small gift because he was thinking about me, a text at work to see how my day is going etc. means that I know he is thinking of me when I am not there. That makes me feel special. Most of all, just hang in there, she will start to become more secure in time.