Dealing with Bulimia personally, i can share with you a little bit of my experience with family who just wanted to help.

If she says she feels fat, dont tell her shes not, just understand that that's how she feels.
If she doesnt want to eat, trying to talk her into it or force it on her will only make her try harder to not eat.
Let her know you support her fully, and that if she ever feels like she just needs to talk, you're always there to listen, and that you won't criticize.

those are all of the things i wish someone would have done for me. Knowing that you deal with bulimia too, im sure that you already know about all of that.. i dont think you would be being a hypocrit if you just let her know that you are dealing with the same things and that its easy to talk to someone who's already on that same page.

Good luck with everything