I found the people who begged and pressured hard to cope with, try sitting down and writing her a letter saying how much you love her and feel about her, how you are worried that her wanting to lose weight may have become something more than that. Say that you know she may find it hard to talk about it to you but that you're there for her and enclose some details of people who could help.
Do some research, talk to some of the organisations out there and get their advice too where you can give more details and maybe get some leaflets and other information you can put with the letter.
Don't expect too much at first or too soon, the ideal thing with a letter is that it can be there when she does want it.
If you want to chat further then i'm on MSN or e.mail on
[email protected].
I hope it all works out for you both xxx