Mother in need

My mother raised 3 children by herself when her husband committed suicide when the children were 4,6 and 8. The oldest has suffered from alcoholism, drug addiction and bi-polar behavior since he was 16. She always tried to help and be there for him. He is now 47 years old. Until 2 months ago he and his 15 year old boy have lived with my mother. His drinking and abusive verbal and sometimes physical behavior got so bad that I convince her to swear out a protective order against him. I thought that would at least get him out of the house and give my mother and nephew some peace.

Unfortunately my 78 year old mother is now suffering from severe depression since he is gone. She has sole custody of her grandson who is 15 years old. As a side note she lost her middle son to a motorcycle accident some 25 years ago.

Is it normal for someone to suffer depression once they no longer are able to enable such a disturbed person? He is finally out of he house and she is mentally and emotionally worse than when he was there.