Hi, I can understand your concern for rash that is very itchy on neck and under the chin. I can make a possibility of Allergic dermatitis. If she has night itching then scabies can also be one possibility. In Allergic dermatitis there are eruptions along with moderate itching and in more aggravated cases there is appearance of more redness which persist for more than multiple of days. The only precaution you must follow is not to touch, pinch pop or squeeze any of them other wise it can get infected and can cause complications. You can apply medium potency steroid cream application of fluticasone cream. You can additionally take antihistamine benadryl or loratadine by mouth. If the things are not getting better then can meet a dermatologist for further guidance. Take care.