I am sorry to hear you are having this concern with Mogs
There are a few reasons why she might be doing this, but the one that seems most likely is that she has some kind of mouth pain. As she is a young cat, severe dental caries or tooth root abcesses are less likely, but young cats can suffer from quite nasty gingivitis. This is inflammation of the gums, and if she has it you should be able to easily see it if you lift her lip and look at the gum margin. If she has gingivitis the gum margin will be red and swollen as opposed to smooth and pink. There are many causes of gingivitis, viruses amongst them, and gingivitis can be extremely painful - hence why they are reluctant to eat.
Have a good look in her mouth and see what you can see. If the gums are red and sore, you may find feeding very runny mushed up food encourages her to eat, which obviously is great in the short term. In the longer term you will need to get her into your localveterinary practice to be assessed and for an appropriate course of action to be taken. this may well involve swabs to look for viruses, dental treatments and / or medical treatments to sort the inflammation out,
Whilst you are looking in her mouth, it always worth checking her teeth for chips or breaks. Fractured canines are again something we can see quite commonly, the other teeth less so. This will also cause dental pain and require dental treatment to sort out.
If her mouth and her teeth look ok, then the other main cause for her behaviour is nausea. This may just be a litt le tummy that will self clear or could be something more serious that requires antimicrobial intervention. 4 days with liitle food is already quite long for a cat - they don't do well with prolonger periods of anorexia. If she does perk up quickly I would get her to the vet for a check over.
The only other thing that could be going is that (if she is not neutered) she could be in season. Some cats can behave really quite oddly in season. However their behaviour should return to normal once they are outo f seaosn. Seasons only usually last 3-5 days in most cats, although some orient breeds are prone to much longer ones.
If you would like more information once you have looked in Mogs' mouth, I will b e more than happy ot help you further.