For anyone with a similar request, we found this bit of code to work perfectly for just the last 6 days and nothing else before or after:

   function isCorrectDate(n) {
   var daybefore = new Date(new Date().setDate(new Date().getDate()-6))
                var today = new Date(new Date().setDate(new Date().getDate()))
  
    return (n>=daybefore&&n<=today);
  }
  function checkDate(n) {
    return[isCorrectDate(n),""];
  }
  function checkField(input, inst) {
    if ($(input).closest('li').hasClass('myDate')) {
      $(input).datepicker("option", {beforeShowDay: checkDate});
    }
  }
  $.datepicker.setDefaults( {beforeShow: checkField} );