How to recover from an eating disorder when you compare your eating habits with your sister?

I've been trying to recover for a while now but I'm finding it REALLY difficult. My sister doesn't eat anything throughout the day besides dinner and for breakfast and lunch she has a cup of coffee. Since I'm trying to recover when I see this it's really hard for me to not compare my body and eating habits to hers. I then think I'm fat or I'm eating too much and need to start restricting again so I can be as skinny as she is or have as flat of a tummy as she does. Has anyone else dealt with this as well? I really need some tips on how to get past this and move on with my recovery!