Well, my story goes:-
I was thrilled to have a MIL. My mother is on a different continent.
I redecorated a spare room which is "hers" alone. She left clothes and stuff in the room to save her carting it up every time. I was absolutely fine with this as it made sense.
Bought all the foods and drink she likes.
Planned lots of outings and trips to keep her amused (she loves getting out and about).
Never let her pay for anything (she's an OAP on a very tight budget).
Paid for her flights and travel.
Watched TV programmes I didn't like because she didn't want to miss them.
Listened to her stories which got more familiar as the years passed and they were repeated.
Even thought about asking her to live with us (we had the room) when she mentioned she got lonely living alone at times.
Made sure DH remembered mother's day and her birthday and we got her something nice.
She wanted to bring a relative of her up a couple of times so they could enjoy their holiday together. Again, I was absolutely fine with this. I loved her relative.
But I wondered why I'd bothered when the passive-aggressive jabs and snidey remarks started whenever DH wasn't in the room to witness them. I've got no idea what the problem was or what I was supposed to have done to deserve being spoken to like that in my own home.
It will forever remain a mystery, I suppose.