Maybe your dad wasn't horrible when they 1st married/met, maybe he hid it. Maybe she misses the man she fell inlove with, maybe she had hope he would change in the future, and is grieving that?
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Maybe she's angry at him for the way he died, maybe she's angry that she didn't get a chance to do the right thing... Maybe she's mourning bcoz she feels lost, her life had a clear pattern for 30yrs, not a pretty 1, but a pattern nonetheless, and now it's gone...
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I honestly don't know MV, I'm just speaking from my experience, tho he didn't die, I left, but I still mourned for the future I had hoped for, for myself and our daughter. And that alone made me angry, at myself mostly...
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I know what you mean about losing both parents that day, I'm living with a shell of what used to be my mother for the last 2yrs, and it's heartbreaking.
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Sorry if I'm unhelpful, didn't want you to feel alone.