my guardian called me fat?? *rant*

Cheyenne
So I was trying on dresses for a retirement party I need to attend for my one guardian (we'll call him Tony) and the other guardian (we'll call her Cindy) when I asked her if the dress I was wearing was okay, she looked me up and down and says 
"that was one I bought you four years ago for 8th grade graduation. You've gained a good bit of weight and you need to lose it. So I suggest unless you plan to lose weight anytime soon you throw that out." 
I've been struggling with an eating disorder on and off for six years (I'm 18) and she knows this. I don't know what to do, part of me really wants to fall back into it again so I can look pretty again because I don't like disappointing her and I know I already have