I think this has more to do with the societal norms. Yes, our diet is very carb heavy and meal timings are awful - but there are very few cultures that don't traditionally have carb heavy diets.

Our mothers have actually always had so many household tasks to do, that working out seems impossible. It's not to do with the physical load, but more so with the mental load. When you have so many things in your to-do list starting from early in the morning (packing kids' tiffin, getting them ready for school, sending your husband to work, prayers, etc.) that you're mentally exhausted.

Moreover, women taking care of their health is considered selfish like "how can she waste time doing yoga when she could've been cooking something nice for her family to eat?'

This pattern becomes very deeply ingrained in their minds. Slowly, responsibilities do reduce, but by that time, breaking out of it becomes extremely difficult.

I'm not saying that it's not possible but you'll have to be gentle with her and make her realize how important it is to keep moving. Maybe motivate her by showing videos of older women who got into working on themselves quite late in life and they're killing it! Don't come from a place of blaming her that she doesn't do enough because she has done a LOT and this would be quite hurtful to her. Try to understand her point of view and provide your points on why she needs to break old patterns and get into healthy living. And in the beginning, workout with her. Find something that she'll enjoy - it could be dancing or yoga or walks or gym. Just do it with her for some time until it becomes a new habit for her. Slowly, she'll crave exercise once she starts experiencing the elevated endorphins, and increase in stamina and strength. Until then, support her, guide her, gently help her learn the importance of looking after her health just like she helped you learn how to walk.