What is the diagnosis and treatment (and home remedy) for multiple red iitchy blistered skin with pus in the neck for a 4-yr old female child?

Various. Your child may have a bacterial infection. For a home remedy, i would try putting a quarter cup of bleach into a half full bathtub and soak in it, followed by patting the child dry and moisturization. Repeat this three times per week, and seek help if it doesn't resolve.
Several possibility. It really depends upon the diagnosis. Early chicken pox is possible but should be present elsewhere on the body. Impetigo may look like this and requires antibiotic, perhaps topically. A burn or allergic reaction is possible.Thus your doctor may need to see as the treatments icluding home remedies differ.
Early chicken pox? Your child sounds like she may have the beginning of chicken pox. You can bathe her in a tepid bath and add several spoonfuls of corn starch or baking soda to the water to reduce the itching.