The Possessed Target is a Fat Duke's Daughter

When I opened my eyes, frilly curtains flew into my vision. I tried to get up in surprise, but my entire body felt heavy as if it were wrapped in lead, and I couldn't get up right away. Desperate to rise, I looked at a mirror nearby, and what was reflected there was... the figure of a fat child with a harsh expression and upturned eyes. Who am I?!! A story beginning with that, featuring a dieting villainess heroine with a "serves you right" taste. There is an atmospheric yuri expression at the end.