Just wanted to say that this is the exact right place to post your rant. It is so so clear that you love your mother and want more than anything to not feel the way you do. Hopefully with more time she’ll come around. People can surprise you so try not to lose hope. How was she during his illness? I’m sure like you and Joshguy929 said that she is just struggling with the loss of her partner.
What I found is that the illness made me realize that parents are people too. they are just trying to do their best but they have flaws and moments of selfishness. Luckily you have your siblings who you sound very close with! Keep trying! Is there anyway you could talk to her about this? I don’t doubt that what you say is true but definitely try to not be cynical!