Two things...
Most women would never flat out refuse to lose the weight. They would instead come up with a million reasons why they haven’t done it or can’t do it.
Secondly if I woman truly loves and respects you as her man then she will take your lead. Now depending on how sensitive she is, and most these chicks are sensitive as all hell, you might have to soften the weight loss conversation so y’all don’t end up arguing over it but I’m general she will go the the gym with you and try whatever diet you set up for her.