Hi there, Yes, you have my sympathies. The trouble with using hand slaps and the like with a 14 month old are not always quite so obvious in this culture. Hand slaps and spanking on an infant and even up to 11 or 12 can be quite effective as a quick fix remedy for the parent. However, just because they have the desired effect at the time doesn’t mean the parent isn't storing up problems with (and for) that child later in life, particularly in their teens. Physical punishment is lazy parenting and it shows a distinct lack of empathy for that child. The slap communicates, 'just do as I say'!
That said, there are certain things I would look for first, as a form of elimination. Does the infant like the food, is it too warm, not warm enough. Has it been preheated perhaps, adding staleness to the flavour. Understanding a toddler’s preference for food might seem tricky at first. But given their cognitive dysfunction at that age, hardly surprising they might throw away food they dislike, that's being pushed into their mouths.
Infants are always trying to communicate something when they throw things like food. With toys it might be other things. Perhaps they need some attention from the adult. Maybe they have seen this behaviour in other adults or older children. It's about an unmet need for which they are having difficulty communicating..
Next time I would gently tell your mom. 'wait, perhaps the food isn't quite right' or some such statement. Try to get your mom to understand the cognitive dysfunction a toddler faces at that age. Very often adults just haven't considered this at all and are surprised by how ignorant they were. Anyway, hope that helps and best of luck.