Two separate issues. The grounds for divorce depends on whether your state has fault based divorce or not. The Immigration case will require you to prove the good faith of your relationship. You definitely need to contact an Immigration attorney. The I-751 removal of conditions is a very import and delicate matter.
The form that must be used to apply to remove the conditions of your residence is Form I-751. You may qualify for an I-751 waiver if you get divorced, but can prove that you entered into the marriage in good faith and/or you can prove "extreme hardship" or "battery or extreme cruelty." These terms have legal definitions and you have to meet legal standards in order to qualify for the waiver. Timing is also very important. It is important to evaluate factors such as: how long you have been married, whether you have children, whether there is proof of her ill treatment towards you, when exactly your green card will expire, how long it takes to get a divorce in your jurisdiction, and who will suffer hardship if you green card were not approved, etc. Therefore, it is best that you meet with an immigration attorney and develop a strategy that is best for your particular situation. I know my response is very general in nature, but the "answer" to a question like this is extremely fact-sensitive.
If you divorce her before obtaining the permanent card, you will need a waiver of the joint filing requirement. You can explore the grounds for divorce with a family lawyer licensed in your state. Some of her threats may be grounds for extreme cruelty ground for divorce ( especially if she has threatened to kill you).
This answer is for informational purposes only and should not be construed as legal advice.