Curvy Wife Thinks She's Become Obese

A frustrating problem for us (and me) lately is that, having gained a few (5-8) pounds, Brenda thinks she is obese. She never felt this way before and the few pounds she has gained do not add much of a difference to the way she looks.
My wife is curvy; she has the kind of figure that stars in the old Hollywood movies had. In addition her once small waist has remained small enough to still highly accentuate her wide hips and protruding rear end. Hers is still an "hourglass figure." I love this and always have. She herself never minded showing off her well-endowed figure (sometimes this became a problem for us). She never hid her body from me; she enjoyed being naked, asked to go to nude beaches, practiced "naturism" in the privacy of our home, even enjoyed me taking pictures and videos of her.
But now all that openness is vanished and has for a couple of months. She runs to the bed from the bathroom, wears a robe around the house, refuses to let me take out the camera, etc.
Despite my assurances and entreaties, this attitude and behavior continue. I feel sorry for her. Most of all, I worry that her bad feelings about her weight will lead her to do something foolish, for Brenda has always needed to feel she looks desirable. I'm afraid that she will sneak off to a cosmetic surgeon, flirt outrageously, spend tons on clothes, make her life hell, etc. etc.