How do you help an elderly person who does not want help?

I care for my grandma who is 87 years old with dementia. She's a diabetic so has to eat and has many pills to take due to various conditions. She's in reasonable health in that she's still using the toilet and staying dry, able to eat, walk, talk, even carry on conversations on her good days but she has terrible mood swings. By mood swings I mean the slightest thing sets her off so she's literally swinging mad beating up myself, herself, and anything else she can get her hands on. Eating is a huge issue as she has to eat being a diabetic and yet sometimes she loves her food and feeds herself and happily comments on how good the food is but the next she's refusing to eat, throwing the food around and hitting me at the slightest offering of food. How does a person stay calm and are there any tips for having eating time be successful? Also pills are sometimes a problem. Sometimes they are happily taken without an issue and other times she holds them in her mouth to dissolve them. This can set her off from eating but if I do it after she eats, then she's holding pills in her mouth burning sores into her tongue (I've never seen sores but one time recently for two days she said her tongue was sore. I had her rinse with mouth wash for mouth sores to help and it seemed to heal it right up.) I use dissolving tylenols at night and liquid advil as well at night but during the day she's on pills. Any suggestions to help with this besides using yogurt, oatmeal or applesauce to get them down? She just chews everything even without having tons of teeth. It's nuts how much she can chew even with only having her front teeth on the bottom and a full denture on the top.