Answer

Although you made the situation worse by not being truthful with her, your fiancée's self image problem and insecurity problem are her problems. Other than being supportive of her, and being truthful from now on, there isn't a whole lot more you can do other than encourage her to seek individual counseling for these issues.
The bottom line is that until she gets a handle on these problems, and makes the decision to trust you, your relationship with her doesn't have much of a future.

Do take care of yourself. We know this is a difficult thing to go through with someone you love, but the ball is in her court. You can only stand by to see if she wants to continue to be with you.

Proceed to the next question.