Hi mama, I don’t think more drinking has anything to do with falling down. It may just be so coincidental that she’s entering the growth spurt leap (usually 6mo) where she tends to feed more. This usually last about 1-2 weeks depending on inidividuals.
Also, it might be because your grandma fed her soya sauce and since she can’t drink water yet, she’s feeling thirsty hence the extra feedings.
I wouldn’t pack and go back immediately, I would sternly warn her not to do that. And especially since she’s my own side of grandparent, I’ll just tell her what I don’t like. If you cannot follow or insist to continue doing so, then only I will pack and leave because you do not know what is respect.
For my case, it was my mil who tried to offer my baby a nip of roast pork at 3mo. I told her NOT to feed my baby anything including water. Regardless of baby food or whatsoever, do not feed her anything without my consent before 12mo.
But yes, as expected, after 1yo, she just feed her all sorts of strawberry cake, abit of whatever she’s eating but since after 1yo liao I close one eye. Perhaps you can try letting them know that you would like them to refrain from feeding your child anything below 1yo. Because grandparents tend to “love” their grandchild and just give without controlling.