It's not a question of you are "no better than your sister" You both have an addiction. Does that make you or her bad? No...not at all. ANY addiction is NOT about lack of control or a moral defect. It is strong...it is soooo strong and just recognizing it and wanting to get help are very positive things. I hope that your realization will help in healing some of the anger you have with your sister.
Guilt and shame, low self esteem, low feelings of self worth...Yup, sounds like the types of feelings a drug addict goes through when he or she wants to quit but the pull of the drugs is too much.
"I know I can do this on my own if I just try hard enough" How many times have we heard our addicted love ones say that. Many of us laugh and ridicule...just a bunch of lies...Yet how many times have any of us with some addiction...cigarettes, food, work, etc. said I know I have the will power to do this on my own and we couldn't...Are we failures? No Are we liars? No Are we poor excuses for human beings? No. We sometimes just need help and if we get the help and commit ourselves to the process and truly CHOOOSE to recover and work it really hard, we can recover. And as we recover, we start feeling better about ourselves and the guilt and shame slowly evaporate...
I feel so strongly that the more loved ones of addicts can understand it is not about lack of love or willpower or lack of morals and find compassion instead of anger and ridicule, the more we can recover ourselves...because those negative feelings just make us sicker and sicker.
Sorry, I went off on a tangent because somehow I still think I can change people and make them find compassion for addicts...more work needed on my part! But I hope you can accept that food addiction like any other addiction is a serious medical condition and the "right" specialists can help you to help yourself as long as you are ready. You are a wonderful, wonderful person and you deserve all the best. You deserve to recover. Hugs and prayers.