Not at all. Your mother’s behavior will have ensured that you experience her death this way: through years of manual or verbal abuse, as well as through its alleged denial. People who abuse others never stand by their actions, but portray them either as a healthy reaction to a hostile environment or claim that the abuse never took place. So the victims are humiliated again. Many of them show self-damaging behavior afterwards because they have experienced such a fundamental devaluation, and not a few treat their own children just as badly later. You can be proud when you have managed to show yourself, your partners and your children the respect that you have been denied. Unfortunately this is the exception.
The reason you call your mother’s death a liberation is probably because she definitely can’t do anything to you anymore. You probably had distanced yourself a long time ago, but now you have nothing more to fear; no chance meeting, no phone call and therefore no memory of the crimes and no more lousy excuses. So your feelings are very understandable. It is also understandable that you should ask yourself whether you should be ashamed of this – actually, you should show respect and love for your mother and now mourn her. That would be the natural state. But your mother destroyed it herself. She is responsible for the fact that her passing is a relief for her daughter. There is no right for parents to behave as one will, and for children there is no duty to tolerate all behavior. Your feelings are absolutely valid – and sufficient. Nothing more is necessary.