Tell the staff you'd like to work with them to put together an intervention plan that will help your mom feel less anxious and upset. Ask the director which staff member you should work with and plan on spending some time at the home for a week or two to get at the root of what's upsetting her.
Ask a lot of questions -- both of your mom, if she's able to respond lucidly, and of the staff -- to figure out if she's just high-maintenance for the facility (or for certain employees) or if she truly is out of line. If her difficult behavior is a recent development, what's changed that could be causing it?
A great first step is to schedule a checkup with her doctor. Her behavior could be caused by something as simple as a urinary tract infection, which can be very uncomfortable and upsetting. Is she dehydrated or hungry? Is she in pain?
Get her to a neuropsychologist, too. If your mom is anxious, sometimes such an expert can prescribe a medication that will keep her alert and functioning but take off the emotional edge. It could also be that your mom's dementia has worsened -- people with dementia are often agitated and combative. If you think this is the case, talk to the staff about whether she should be moved to a dementia unit.
If you rule out medical and clinical problems, you can look at environmental explanations. Ask the staff under what circumstances your mom starts acting out. Does she have a roommate she doesn't like? Do noises, such as music and phone calls, bother her?
Once you have a sense of what's troubling your mom, you can start to work with the staff on a plan. I know a sweet 90-year-old grandma who nonetheless kicks her fellow residents. The staff figured out which residents irritate her and the best ways to distract or redirect her attention. And they know she needs to sit by herself at meals. If your mom feels lonely, bringing in a companion --available friends or a paid caregiver -- to spend time with her during the day may do the trick. If she's understimulated, getting her engaged in an activity she enjoys might help. The key is to let the staff know you're committed to finding a solution.