Maybe there is some truth in it: https://www.straitstimes.com/lifestyle/leftover-food-to-eat-or-not-to-eat Many people think that heat as well as cold temperatures will keep food safe, but this is not always the case. A common example is the idea that leftovers are safe to eat once they are heated. However, as bacteria multiply quickly in temperatures between 5 and 60 deg C, food that has been left outside the fridge for too long may contain a lot of bacteria. Even boiling may not be enough to kill the bacteria, said Professor William Chen, Nanyang Technological University's Michael Fam Chair Professor and director of its Food Science and Technology Programme.
Bacteria and mould starts to form when food is left out over 3-4 hours, it’s a fact, sometimes for soft and wet food, you can start to smell “rubbish” smell, or things that contains coconut or milk becomes extremely sour. I’m surprised you want your hubby and kids to eat that. Adults may have some immunity but for kids botulism kills. It’s not worth to save that extra dollar for hefty hospital fees. It’s penny wise pound foolish, so your mil is not wrong. For rice is still ok when in rice cooker, transfer immediately to plastic bag and fridge and can fry next few days. Other than that just dump the rest of the food.
My POV, no right no wrong here. Why not cook lesser? That way no leftover = no tension no debate. If your MIL is the one cooking and refuses to lower the quantity resulting into food waste, then make sure she pays for the food. Only when you pay and feel the pinch everytime you see it in the bin, then you’ll do something about it. At least it worked for me 😅
curries taste better the next day. and how did u cook fried rice if its not leftover rice from yesterday? this is sad in many ways. leftovers are still good if properly kept and refrigerated.
Better to just let your MIL be while doing what you want when she is not around. These are the times when little white lies have merit 🙂
Cook what is needed. Fresh food is always good, i will prefer it over leftover.