Wow firstly i think its great that you'll be there for her, but make sure its for the long term! Having been that friend myself i found that at first i received a ton of attention and concern, and then as i actually started to get better my friends seemed to back off and eventually ignore me completely, which made me feel awful and like i actually needed the eating disorder to have friends!
Yeah try and arrange things to do with her that have NOTHING to do with food or things like swimming, as soon as my friends realised i was gaining weight they started to want to go out for meals to 'help' me, usually eating with others causes extreme anxiety to those with eating disorders and can actually lead to compensatory behaviours (purging or restriction before).
Finally just ask how she is feeling about things, if you must make comments then say 'you appear happier', nothing about her appearance, even comments like 'you are looking so much healthier' can be immediately translated into 'you are starting to put on loads of weight'. Remember the eating disordered voice fears being a 'healthy' weight.
And lastly just remember that she is still just your friend, she is not your anorexic friend and therefore should not be ostracized. She has an eating disorder, but this does not define her, in fact it is a small part of who she is. Help her to develop the better part of herself =]
xxxx