What do you when your aging loved one is very uncooperative and you have to coerce her or him to eat?

Let her eat the food late. Why spend energy only to be frustrated when she ends up eating anyway, just at a later time?

If she doesn't want to eat, don't force her. That's the surest way to get someone NOT to eat.

You haven't filled out your profile so it is very difficult to guess what is going on.
Does your loved one have dementia? Is she giving you a reason why she doesn't want to eat? And what exactly do you mean by coercion?
Changes in taste caused by medication or simply aging, restrictive "healthy" diets, difficulty with eating certain textures and overwhelming serving sizes can all cause someone to reject their meals, it can also be a significant end of life sign. Can you give us a little more details?