I'm so glad to see other people use TE for these kinds of problems. Sometimes it is so nice to get in here and vent a little to people who don't have a stake in the situation.

Maybe she has always been like this but is getting worse in her old age, and as you noticed losing your Dad had a big impact on her. I've noticed an irrational insecurity in elderly women. My grandma was convinced that she was going to be out on the street, after Grandpa died. Of course Grandpa had provided for her, and none of her kids or grandkids would ever allow that to happen.

I guess the care taking of elderly relatives can invoke a lot of guilt and resentment, from the care takers, the ones who are too far away, or unable or unwilling to help more, and the elderly relative. The feelings probably aren't fair.

My advice (FWIW) is to think of Grandma as a sick person. It's easy to say "She's always been like that" and blame her for being unreasonable, but even if that's true, she's gotten worse, she hasn't really always been like that. On the other hand take care of yourself, don't visit her as often if it upsets you.