Grandmother won't eat meals and only wants to constantly snack all day and night.

Let her eat what she wants when she wants.

Your grandmother has dementia and is 93. Enough said.

If a 93 year old wants to eat candy, let her eat the damn candy. Are you afraid she won't reach 110?

You are living with grandma and you are the one that is providing food for her.
With the Dementia she does not "get it" when you tell her that she needs to heat a healthy meal.
So stop worrying about a "balanced" 3 meals a day.
Give her more acceptable snacks that she can have more often.
If grandma is mobile and making her own meals that is another story.
Is she competent to make decisions? Or is someone POA for health, finances? If she is making her own decisions you have little to say about it.

Honestly with all she has going on health wise I would begin to worry less about things. She is 93 with Dementia, mobility problems, heart disease and the list goes on.

My father had diabetes for 40 years, he loved cookies and sweets, so he ate them, he died at 84 of lung cancer.

Leave her alone, she is in her 90's, at that age what difference does it really make what she eats?

My mother is 98, she eats whatever she wants and I support it.

Your grandmother is 93 years old for Pete's sake. Let her eat whatever she darn well pleases.
What are you afraid of? That she's going to die if she eats only junk? Well guess what? At 93, she's going to die sooner than later anyway, so let the poor woman be.
If someone tries to tell me what I should or shouldn't be eating at 93, I would tell them to get the heck out of my house or room if I happen to be in a facility.
Please let your grandmother enjoy whatever time she may have left on this earth, and eat whatever the heck she wants to!

If this is how she's been eating all her life, she probably won't change her ways now.

She is 93, let her eat what she wants. My mother was diabetic and refused to eat right, even when she was in her 60s. We had a family meeting, asked her if she wanted us to keep trying to get her to eat healthy or leave her alone and let her die sooner. Yes, those were almost my sister's exact words. Mom said leave her alone, so we did. She lived to be 85.

From your profile:
I am caring for my grandmother living at home with age-related decline, alzheimer's / dementia, arthritis, diabetes, hearing loss, heart disease, incontinence, mobility problems, osteoporosis, and vision problems.

About Me
I'm a 49 year old woman who provides 24/7 live in care for my 93 year old grandmother. This started as a part time thing. My mother, her daughter was helping as well. However, my mother had multiple strokes and hasn't been able to care for her. I stepped up the past year and a half and it has turned into 24/7 ever since. I've not had a single day off. I'm the only one to care for her. Her son, my uncle works full time job and makes all the financial decisions. I have been doing this with hopes that she wouldn't have to be put in a care facility. I have always been very close with my grandmother and have tried to be the hero, but it has seriously taken a toll on my health and mental health. This is just so much on one person. 

With dementia at play, grandma's tastebuds changed and she now wants sweets all the time. Nature of the beast.

With all you've already got on your plate, are you really wanting to ADD grandma's nutrition to the chaos, at 93? I'd either leave her alone to eat whatever she wants or remove all the junk food from the house. Replace it with healthy options but expect carrying on in response.

I don't know why you think it's heroic to keep grandma at home and out of Memory Care Assisted Living when it provides a stimulating environment for her and 24/7 care. You're sacrificing your health and emotional wellbeing when you could visit her daily and become the granddaughter again instead of the burned out caregiver.

Best of luck to you.

She is 93 according to your profile.
That is a tremendous age to reach as a diabetic; are you aware of that.
This disease is so difficult on the entire heart, lungs, kidneys, vascular system that people are almost always dead at this point.
I would get my Grandmother on palliative care, and Hospice when doctor deems it appropriate and I would let her eat anything she wants knowing she is at the end of her life.

Your mother has had multiple strokes.

That should have been a warning sign that taking care of grandma is too much for even two people and now it’s down to just you .

Get help in the home, try to get her hospice and nurse’s aides on top of hospice because hospice isn’t enough to give you respite….. or place grandma in memory care or a nursing home on palliative care . Let her eat what she wants at this point . She has dementia she’s going to crave snacks and treats , plus she has so many other issues .

Grandma doesn’t need a hero to save her . She needs to be comfortable .