I don't know anything about dementia, but my mother is type 2 and is now on a morning insulin injection and due to her elderly sedentary life her appetite is diminishing.
A diabetes nurse told me some people need a few bad relapses with diabetes before they are compliant.
It looks like you need to speak with her Dr and have tests and referrals, tests for advancement of her condition, nutrient deficiencies due to poor diet and any medical issues eg ulcer or whatever from her poor diet and referrals to the swallow team, diabetes team etc, also consultation with dementia team and to find their website and forum for tips.
They tried giving my mother a supplement drink in hospital a couple of years ago when she had no appetite after a stroke, she didn't like them, said they made her feel sick - I looked at the ingredients and there was about 32g of sugar in it and it was a tiny bottle, I tried a few sips of one and it was very sickly. They complained about her blood sugars being high like it was my fault, then I asked them if they knew how much sugar was in these drinks they're giving her! No joined up thinking - give her calories to build her up - her blood sugars are really high...duh! That stopped them! if they persisted in blaming me I would have told them to do the blood test for her averages and taken her test meter in for them to see the averages on it showing her well within range over 3 months.
Does your wife like milk? our Dr said milk has a lot of what she needs, so she has cereal in the morning with full milk, a third full milk in her coffee and a small glass of gold top in the afternoon. He also advised not to make meals a battleground, have something for her to eat later and be prepared for her to reach the stage where she is grazing snacks rather than eating meals. Milk and cereals are frowned on by the practice nurse for diabetes but the Dr overruled it because she isn't eating much and needs that supplement. Her blood sugars are within her range and are often lower than that range due to her low appetite and her insulin was reduced recently. But this is a frail elderly 90 yr old lady with a sedentary lifestyle due to worn out body, heart and chest.
Is your wife good at taking tablets? Can you get her blood tested for anaemia and other deficiencies? My mother is prescribed iron tablets, vit d tablets and vit b injections and a few times a week I give her a multi vitamin and minerals tablet.
is she showing signs of an ulcer? or other issues from poor diet making her less keen to eat/making her feel sick? that is a concern, unless it is an excuse to please herself with her food. I know of two people whose mother and mother in law hid food away, wondered if it was being saved for later, then transpiring they were hiding the fact they didn't want to eat/eat it particular food.
Do you test her blood sugars with a lancet and testing strip? or has her diabetes not got to that stage yet? have you spoken with her diabetes nurse or GP? have they told you what to do if she overdoses on sugar?
Have a look in the diabetes uk forum, there is also advice in there regarding low sugar foods
Unfortunately many sugar free products have sweeteners and some of those have a laxative effect.
There are packs of sugar free jelly crystals which are good and easy to make up, you can add a sparing amount of fruit to them.
Have you tried leaving a packet of crisps out instead, I know, they're carbs, but worth a go, try prawn cocktail flavour as it is sweet, I give my mother half a packet as they're carbs.
Those biscuits Susieq mentioned are good but in moderation, I give half a biscuit to my mother, she doesn't care for them, they aren't sweet enough for her. We don't have sweets or chocolate in the house. No jelly babies in case she goes hypo, her Dr said a bit of jam on the end of a spoon would be better because she hasn't got to make the effort to chew. We don't have jam in the house but we have a little pot of it and I made plum jam last year with a third sweetener in it.
My mother has difficulty swallowing tablets and drinking some fluids for about 6 months after strokes and then less so but she will still have issues at times. it is down to the swallowing and breathing mechanisms, the swallow team explained it to us then did an examination of her and explained her issues and gave techniques to use.
My mother hates any drinks that are thicker than white coffee or milk, she finds them difficult to swallow and feels like they are getting stuck in her throat and/or not going down. Again this is due to her swallowing mechanism being messed up from the strokes, this is Dysphagia and it affects those with dementia, if the symptoms are like those in this link you need to get a referral to the swallow team who might be able to help
https://www.nhs.uk/conditions/swallowin ... dysphagia/
She hates soups but loves my tomato soup, using sweet vegetables I add a pepper, a few carrots, an onion or leek and some swede or sweet potato, I get it to the right consistency for her and on serving I add a little bit of sweetener and serve with a couple of toasted cheese straws or some wotsits to sprinkle on top. I freeze the rest.
My mother has a very sweet tooth but allows me to control sugar for her. She's had several mini strokes (TIAs) and now her appetite is diminishing, I give her child size portions and on a good day she can eat half of that, on a bad day she just picks at it, saying she's full. This could be due to the effect of the strokes on her brain and/or the ageing of elderly body not needing much food now.
