Stop feeding milk. Cats do not have the enzyme lactase that is needed to digest lactose which is present in cow's milk. This can cause diarrhoea and tummy upsets.
Also, I'd leave off too much peanut butter, keep it for treats or if you need to get your cat to take medicine. It's a high source of fat, which is not bad in a cat that is not eating, but it's better for your cat to be eating meat. The peanut butter itself may be making your cat feel ill. So try without it and see what happens.
If she hasn't been wormed, she may need to be wormed, as a high worm burden can make kittens and cats ill. It can cause a lack of appetite.
She will also need to be vaccinated if she leaves the house, or comes into contact with other animals. Many of the illnesses common to cats can make them ill also.
From St Ives Vet (a local vet to me)
Cats can be infected with roundworm, hookworm, and tapeworm. Large worm burdens can make your kitten very ill. They can also infect people. When you first obtain your new kitten he/she should be wormed immediately and then again ONE week later. Your kitten should then be wormed every 2 weeks until it is 12 weeks old and then monthly until it is 6 months old. Intestinal worms are rarely a problem in adult cats. The recommendation is to worm adult cats every 3 months. Products such as Milbemax tablets, Revolution topspot and Profender topspot are all effective against all worm types.
It will be important to save to have her desexed or to find some organisation that can do this for free or for cheap, as a pregnant cat and kittens will put more strain on the family budget.
Also from St Ives Vet
Your kitten should be vaccinated at 6-8 weeks of age, 10-12 weeks of age, 14-16 weeks of age, and then annually for life. We routinely vaccinate kittens against:
If you have missed vaccinations, then two should be sufficient to provide a lasting immunity. As for the annual booster, this may not be necessary for the cat's health, but is for kennelling cats at catteries in many places.
The other thing is to check for parasites. A high flea burden can cause anaemia. Ticks can also make cats very ill and can be fatal, depending on where you are living.
they cause loss of appetite, vomiting, difficulty breathing and paralysis starting in the hindlegs.
I congratulate you for taking such good care of your kitten and the time to search and seek help. Please let us know how she gets on.