Thanks for the update @Christine. It sounds like your mother has successfully secured her position in your agreement. I think keyholders reading will be encouraged to choose waist rather than hip model belts in the first instance.
From your perspective I think the only way for you to change the arrangement is to keep on talking with your mother about the belt and her reasons for using it. Do you talk about it when swapping the belts over etc? If you do this, over time, her view and yours may soften and become more moderate.
Until then, I hope you manage okay with the new belt.
