I'm going to go with what a lot of people have already said : she's insecure about her weight and the thought of you knowing exactly how heavy she is upset her, rather than anything you actually did. Possibly she thought that as long as you didn't know exact figures, it didn't matter.

[Dan Savage](www.thestranger.com/savage) has some good advice about this sort of thing. I can't find a specific article, but basically : tackle it head on and try and get into a conversation about it. Tell her, in no uncertain terms, that you love her no matter what she weighs. You loved her before you saw the scales and seeing a few numbers doesn't change a damn thing.

Then ask her how she feels - it might be that she's incredibly unhappy with what she weighs and has been trying to lose weight unsuccessfully, which is upsetting her even more. If that's the case, make sure she knows you're on her side. If she really wants to lose weight, get in on the act. Eat the same (healthy) meals as her, go to the gym together (although it sounds like you're already doing that), and above all, make sure she knows you're supporting her no matter what.

Basically, as long as you let her know you love her and support her decisions, she'll probably come around.

Oh, and let us know how it goes :)