A man is not entitled to have sex with his wife just like a woman is not entitled to a husband who makes six figures. You really do get what you sign up for though if you put in the time to get to know the person. In my dating days, there were women who would hold sex over my head. I passed on those women and often cheated on them during the relationship more out of spite than anything. If you choose to marry one of those women, then that's just as much your problem as it is hers. I know my wife would not use sex as a bargaining tool, punishment or form of control just as she knows I won't use my money or physical strength for the same things. We dated for about 4 years and knew this about each other before getting married.
On to the focus, I have a hard time believing she killed him. If there was someone else involved, maybe it could've happened. She's probably around 5'4"-ish, ~110lbs, maybe? He was a brutal championship prize fighter. The theory is that she hit him in the back of the head with something to knock him out and then choked him to death. The autopsy found a cut in the back of his head but no evidence of new brain trauma. I don't know that anything short of a cracked skull from a bat or a hammer would've knocked him out and she couldn't choke him out if he was at all coherent.