@yannickq That's what I thought at first too the way it was drawn, but I went back and checked and Yama gives her two things: a necklace with 4 "jewels" and a yellow candy. He explains the red, blue, and green jewels, and he's about to explain the yellow when she eats the separate candy which transports her.
And agreed it's pretty ridiculous she did that. You wouldn't expect someone with impulse control that bad to be able to diet and exercise for six months that effectively.