Every day is different, what is wonderful one day is rejected the next, mum would often like 3 freshly cooked meals put in front of her at every mealtime so she can choose what she wants from the menu, not practical and financially not too clever either, but we keep on going. She can still feed herself but will go into 'baby mode' where she wants to be fed, a nightmare.
We go through bad patches when she wants to give up, I rely on my best friend in the kitchen, unflavoured Complan, apparently undetectable in food but makes things taste creamier. When the porridge is cooked in the morning i try to get it cooked as long before she gets up as possible, can get lots of milk absorbed that way, then reheat in the microwave, add sugar and Complan, stir very well to get rid of the Complan. Dinner time have soup in the freezer - Tesco own brand from the chilled cabinet freezes fine, tinned soup always seems too salty and there is a detectable tinny/chemical taste in some. Can get it from frozen to serving in 10 minutes, add Complan for nice creamy soup. Homemade mashed potato is a good way to pack in calories with flavour - milk & flavourful cheese, maybe a smidgeon of Complan. If you have mash left over put it in the next lot of soup. Homemade oven chips with light olive oil, add something like barbeque seasoning, lay off the salt. Soya sauce in moderation seems to stimulate the taste buds - Katsup Manis makes mushrooms taste more mushroomy, it is also a bit sweet tasting when mum doesn't want savoury.
Fresh fruit and nice icecream works well - for some reason she seems to go for Mackies vanilla, I think it isn't overly sweet. Fruit cooked in honey with cinnamon, put on top of a slice of sponge or carrot cake, splodge of sweetend live yoghurt using honey and vanilla disguises all sorts of things.
It is a battle but I had a practice run a few years back when mum got cdiff, thought she was going to die, got her out of hospital but she had been reinfected so it came back, we dealt with it at home, felt we had nothing to loose and preferred she died in her own home if it came to that. Cdiff makes people not want to eat, it seemed very much like the dementia eating problem but with things running out the other end in a very horrible way. Used the above feeding methods to pack in the calories and vitimins, it worked much to the suprise of the doctors who had told me I was fighting a lost cause. She has now got to 96, still mobile.
A common denominator with cdiff and dementia feeding problems in our home seems to relate to what is on the plate, small snacky things, lots of individual flavours, a full plateful of food can turn mum's stomach - but then when things normalise with her she will eat huge amounts of food off the plate. Remove the cup/plate and she can sometimes nod off and when she wakes thinks she hasn't drunk/eaten, can get an extra cup of tea down her and sometimes a second breakfast.
I don't know if any of the above is of any help, problem with dementia is that everyone is so totally different. Good Luck. It is a nightmare and you feel so helpless most of the time