I’ve found a manga that has a female weight gain and weight loss, it’s call: ‘Yokai Doctor’.
In Volume 10 Chapter 72 has female weight loss and weight gain in pg.6-9
https://m.dm5.com/m90701-p6/
In Volume 15 Chapter 99 has a female weight gain where Kotoko get possessed by four Yokai spirit that turn her into a fat Chibi version of herself in pg.136-141
https://m.dm5.com/m90704-p70/