I'm very sorry to learn about your dad, such stories are always horrible to hear.....
But i disagree with some things you did. Your mom was already very stressed it was kinda normal for her to try and take her frustration out on you. My mom does it all the time when she had a bad day at work. But do you really think it was worth fighting your very own mother just for one day off PC?...IMHO it was OK to defend your right to use the PC, but when she started touching you, you should have understood she was very determined and hysterical and just left the place quickly. I dont agree with your mom either, she should never have "attacked" you. But i think its understandable...she just learned her husband was doomed to death....
Blocking her attacks/running away, OK. But trying to master her using brute force? No way.
How are your other family members reacting about this? Are they blaming you, or her?