It is odd for such a young king to go off feed. My adult kings will take food breaks during breeding season and during the winter sometimes. My Cal King has only eaten 3x in the last 4 months but he's still active and not losing much weight. Are your prey items hot enough? Once thawed I use a blow dryer to heat the prey up to about 100F before I serve them to my snakes. It sounds like your temps are on par so as long as your husbandry is dialed in and the snake isn't losing much weight I wouldn't worry just yet. At 4 months I'd think your MBK would be eating larger prey. If she refuses a few more meals you may want to try braining the prey item and if that fails you could try a small live feeder. Sometimes a live feeder will kick start their appetite. Best wishes and keep us posted.