Undergarments for MOB gown

Hi Ladies,
My mom is a size 12-14 and her problem area is her belly. Where can she go to get those undergarments that she can wear underneath her dress to maybe 'hold all that in'

Any ideas? The place she bought the gown does not sell them, and she wants to get them before her fitting.

Thanks!

Kohls has them, bratenders in the city.. you need like a corset body shaper ( i wear them during the regular week! they are comfy) I think blums might have them in patchogue?