Hi - my name is XXXXX XXXXX I'm a Criminal Law litigation attorney. Thanks for requesting me! I'll be glad to help.
It's still not too late to file a police report and to file charges against your boss's daughter in law for assault and battery. That's likely the most prudent thing to do at this juncture. As long as you didn't strike her, there should be no basis for a retaliatory claim against you for the same thing.
Then, you could use this incident as a basis for your "good cause" to quit your job. Generally, if you quit for good cause, you can be eligible for unemployment benefits. Here's a good link that outlines the reasons/basis for one to quit a job and still be eligible for benefits: http://www.nolo.com/legal-encyclopedia/unemployment-benefits-when-quit-32450.html
The most likely argument you would have is that you've basically be driven/forced to quit because conditions have become too contentious for you to remain.
Filing the criminal charges will certain solidify your concerns and provide solid proof that your concerns and the actual hostility of your workplace does exist.
What are my chances to prove the workplace is hostile with just the letter of apology from my Boss?
That fact that your boss's daughter in law slapped you, the letter and your testimony are all very good proof that there is contention and unrest.
The fact that your boss has a specific reason to treat you differently - because of the altercation with the daughter in law - is strong if that's all you had.
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