I once heard that it’s brought down somewhere that a MIL and DIL naturally don’t get along because the DIL takes over the son and continues to take care of him and she gets any furthur Schar.
I’m not sure if this is legit, and if someone knows more about it, please share. It happens to make sense though.
I B”H get along beautifully with my MIL and most people I know also do. So maybe it’s just time for a change in attitude?