Getting worse with dementia. Help!

My mother in law is getting more & more violent..nothing you try & do is good for her. Everything is just NO!NO!NO! She does not know me at all..swears ugly words to anyone that comes to greet or try to kiss or touch her...its not nice anymore. She does not want to eat or drink anything..if you try making her drink some complan or soft porridge, she spits it out onto the floor & laughs about it. When u try to wash or shower her, that's when the trouble starts. She grabs you where there is soft flesh & locks her fingers into your skin & it is so difficult to get her hands off you, you can't try & loosen her grip cause her arms starts to bleed because the skin is so thin. God forgive me. You end up with scratches & blue, purple marks on your face, arms, neck, back & even your thighs. I thought by not eating you would get weak & get more calm. No not this woman, it seems she gets even stronger. By the way she is 84 years old &  weighs 47 kg....help!!!!