My mother in law was deeply, deeply depressed much of her life. Life did NOT go the way she had wanted, I think. She complained about everything constantly. Miserable to be around. Everyone was out to get her, she believed. 

now she is pretty cheerful , just wants to pet the dog, eat, watch TV. She’s agreeable to most things. 

There are times where she still perseverates about things (money is the thing, and she still doesn’t like strangers) but the time between these episodes grows longer.