We put my 92 year old father on a low dose of Zoloft (25 mg.) about a week ago, to see if it would help his incredibly mean verbal abuse that seemingly comes out the blue and is always directed at my husband. So far, it seems to be working! He has had anxiety issues for YEARS that never were addressed; OCD issues that were never addressed either so we also have to deal with that.
But I cannot recommend enough that you speak with your elder's internist and ask about prescribing a low dose of antidepressant. The elderly seem to tolerate and metabolize these well and if it makes them a bit more happy and less crabby, combative and verbally abusive....what could be wrong? DO IT!
Do what must be done so you can live a happy and peaceful life. Nothing you can do will bring peace or happiness to your mother, so you simply look out for her safety. She needs to be in a place where her needs can be met: physical, social, medical, psychological. You can't be all those things to her. She may very well respond quite differently to other people - especially people in scrubs who look like a medical person or authority.
Your strong individuality is a gift and blessing that will get you through this. You deserve a happy life and that is NOTHING to be guilty from.
If you can't make the needed changes for your mom, leave it in the hands of the county social workers. Like Jeanne said, GO IN PEACE. You have done what was possible.