How to deal with younger sister developing an eating disorder while I‘m struggling myself

I (20F) have had very disordered eating patterns, mainly manifesting as restriction, for a few months. Since being back home from uni, I’ve payed attention to not let it show to my younger sister (17F), but I‘ve gotten noticeably thinner and eat smaller portions. Now, I‘m starting to see changes in her behavior — different, more restrictive eating habits and now also having ordered a body scale. I feel like I‘m seeing a replay of my exact situation.

This is really getting to me on several levels. Most of all, I feel very worried for her and am scared that she will develop in a way similar to me. I can‘t help but blame myself for putting thoughts like these in her head, especially through my portion sizes and family members commenting on how skinny I am. As her big sister, I am supposed to protect her.

At the same time, the toxic part of my brain is comparing myself to her. We are identical in height and very similar in body type. I am so so worried that this whole situation will manifest into some sort of competitive eating disorder. More than anything, I want to help her.