My mom has become verbally abusive and violent. What should I do?

If a UTI has been ruled out then that is often the time that your loved one needs to be placed in the appropriate facility and in your moms case more than likely a Memory Care facility.
Violence or abuse of any kind should never be tolerated by anyone, so start looking around today to find a facility that will take her. Her doctor may have to prescribe a medication to help with her violent outbursts before any facility will offer to take her however.
Best wishes in getting this all figured out.

You should call her doctor for a consultation and physical exam. She can have something wrong organically like a UTI which would exacerbate her dementia symptoms and even cause violent behavior, or, she could be advancing with her dementia and need meds to calm her down. You can call 911 next time she physically assaults you and have her transported to the hospital for a psych evaluation, that's an option. Then consider placing her in Memory Care Assisted Living or Skilled Nursing if she's living with you and it's gotten to be too much to deal with, as is often the case with dementia.

Good luck to you.