So I told my sibling I have an eating disorder..?

I confided in my sister that I think I might have an eating disorder, and all she said was 'yeah, I know. I always knew you had some sort of disorder with eating.' So I said, 'why didn't you tell me?' And she replied that it 'wasn't in her place to tell me' but you're my sister! To which she said, 'yeah but not everyone can take it like you, some deny it etc.' so her way of trying to resolve it was telling me to eat ALL the junk food she bought so she doesn't get fat. Wtf. And said I need to drink more soda/ fruit juice to 'fatten up'. I just wish she told me earlier because I've had this disorder for about a year now :( and I wish someone noticed in the family. Is it bad that I'm actually p*ssed off at her? She previously told me about 2 weeks ago 'why don't you eat more food?' To which I jokingly said 'since when did you care?' And she replied 'I don't.' And here, I thought she could help me. But she's acting as if nothing happened. :/