I would try for one appropriate sized meal over two smaller prey items. Many snakes won't take a second prey item.
If she's a rat eater, STAY WITH RATS!
BP's are known to imprint on a prey item and only want that. If she's taking rats, keep her on rats. That will pay dividends when she's bigger. If she has a mouse and decides now that she likes that better, she may hold out for a mouse. No fun giving 5 mice a feeding to an adult female BP.