Hi, its ture that focusing on something else will help but it wont solve the problem. Her problem is her physical apperiance and you have to talk about that!

When my sis had that problem, (bulimia) we talked about the way she looked and i once tried to tell her that she was beautiful form inside and that that is what counted after all, but you must be careful, because doing so she/he can take it wrongly, ie she might thing you are saying,'so wat you are a bit fat, its wats inside that counts', and you must NEVER give that message cause it will distroy her!

Talk to her, she might have other problems other then her weight obsession, since she tried to commit suicide, so talk to her about these problems, you might feel cheesy saying the old stuff over and over again but somethimes it is that which helps. She might want someone to talk to and thats all!

Its good that you have a good relationship, that means she trusts you! So take this to your advantage and tell her that she looks good! That she wouldnt want to get thinner or shill be too thin! Things like that! I mean dont egsagerate but try and help her see herself as beautiful! Im sure everyone felt ugley one time or another, so use that experience to help her out!

You could train together, excersise! i dont know just a few ideas!
Anyways good luck!