Have you ruled out physical difficulties other than swallowing? These could be uncomfortable dentures, tooth abscess, mouth ulcers, oral thrush. How is her sense of smell? It's harder to take an interest in food if you can't smell it, or have a nasty taste in your mouth.
Maintaining fluid intake is very important, not least because this helps to move waste products through the gut. A sluggish digestive system allows toxins to be reabsorbed and depresses the appetite further. Does she still have bowel movements?
The problem with getting her to eat is that she has no understanding of the long-term effects of refusing to eat. We had this with MIL. It was always "I'll have something later" or "I've not long eaten" or "I won't have anything now or I won't have any appetite for my tea". So frustrating, especially as she would eat like a hungry horse when taken out for lunch. By the time she ended up in hospital she was malnourished with scaly skin on her legs due to vitamin deficiency. This despite daily visits from family.
My dad, who did not have dementia, lost his appetite and began to lose alarming amounts of weight. If you don't feel hungry and the sight and smell of food nauseates you, it is understandable that you think you'll wait until you feel better. Eventually my dad got scared by the weight loss and invented his own high calorie diet of cheese, peanuts and Indian snack food (which contains batter and oil). He was not one for green vegetables, milk or sweet things so protein and fat suited his needs.
It is usually recommended to try and encourage grazing if someone can't cope with meals. A small plate or saucer with things they can pick at, e.g. little cubes of cheese, squares of chocolate, slices of banana, halved grapes, jelly babies, squares of fudge, small segments of Scotch egg or sausage roll, a few cooked chips, potato crisps, nuts, raisins, chocolate finger biscuits, marshmallows.
Any calories are better than none. The aim is to stimulate a small amount of appetite and then keep the momentum going. It took my dad about 2 months to actually feel hungry again.