Do I have a case of nursing home abuse?

My 91 year old mother lives in a nursing home. She has Alzheimers and limited mobility. She is primarily wheelchair bound and cannot walk without assistance. Last week the CNA put her on the toilet and left to go to the bathroom herself. Since my mother has Alzheimers she sometimes forgets her limitations. My mother tried to go back to bed and fell. She severely broke her arm (angulated fracture of the humerus) Although the CNA admits to what happened the administration is avoiding me and when we did talk they refuse to call it neglect and are still investigating Many people have advised me to sue. I don't know what to do.